observing the moon. the modern astronomer's guide

Observing the MoonThe modern astronomer’s guide

Written by an experienced and well-known lunar observer, this is a

‘hands-on’ primer for the aspiring observer of the Moon. Whether you are

a novice or are already experienced in practical astronomy you will find

plenty in this book to help you ‘raise your game’ to the next level and

beyond. The author provides extensive practical advice and sophisticated

background knowledge of the Moon and of lunar observation. The

selection/construction of equipment and optimizing of existing equip-

ment for such projects as drawing, photographing and CCD imaging of

the Moon are covered, together with analysis and computer processing

of images, and much, much, more.

Learn what scientists have discovered about our Moon and what mysteries

remain still to be solved. Find out how you can take part in the efforts to

solve these mysteries, as well as enjoying the Moon’s spectacular magni-

ficence for yourself!

gerald north graduated in physics and astronomy. A former teacher

and college lecturer, he is now a freelance astronomer and author. A

long-term member of the British Astronomical Association, he has served

in several posts in their Lunar Section. His books include the acclaimed

Advanced Amateur Astronomy, which has become a classic guide for astro-

nomers wishing to raise their observing to the next level.

Observing the MoonThe modern astronomer’s guide

GERALD NORTH BSc

published by the press syndicate of the universit y of cambridgeThe Pitt Building, Trumpington Street, Cambridge, United Kingdom

cambridge universit y pressThe Edinburgh Building, Cambridge CB2 2RU, UK40 West 20th Street, New York, NY 10011-4211, USA477 Williamstown Road, Port Melbourne, vIC 3207, AustraliaRuiz de Alarcón 13, 28014 Madrid, SpainDock House, The Waterfront, Cape Town 8001, South Africa

http://www.cambridge.org

© Gerald North 2000

This book is in copyright. Subject to statutory exception andto the provisions of relevant collective licensing agreements,no reproduction of any part may take place without thewritten permission of Cambridge University Press.

First published 2000Reprinted 2000, 2001, 2002

Printed in the United Kingdom at the University Press, Cambridge

Typeface Swift Regular 9.25/13pt. System QuarkXPress™ [se ]

A catalogue record for this book is available from the British Library

Library of Congress Cataloguing in Publication data

North, Gerald.Observing the moon : the modern astronomer’s guide / Gerald North.p. cm.

Includes index.ISBN 0 521 62274 3 (hc.)1. Moon–Observers’ manuals. I. Title.QB581.N67 2000523.3 21–dc21 99-044584

ISBN 0 521 62274 3 hardback

Preface vii

Acknowledgements ix

1 “Magnificent desolation” 1

1.1 An orbiting rock-ball 2

1.2 Phases and eclipses 4

1.3 Gravity and the tides 14

1.4 More about the motions

of the Moon – libration 15

1.5 Co-ordinates on the

surface of the Moon 20

1.6 Occultations 22

1.7 Timing and recording

occultations 26

2 The Moon through the looking

glass 29

2.1 The Moon in focus 30

2.2 The pioneering

selenographers 41

3 Telescopes and drawing

boards 47

3.1 What type of telescope

do you need? 48

3.2 How big a telescope do

you need? 55

3.3 Eyepieces and

magnification 57

3.4 Making the best of what

you have 59

3.5 Drawing the Moon 61

4 The Moon in camera 69

4.1 Films for lunar

photography 71

4.2 Tripods and telephoto

lenses, focal ratios and

exposures 74

4.3 Lunar photography

through the telescope –

at the principal focus 80

4.4 High-resolution

photography 84

4.5 Slow films and large

effective focal ratios 92

4.6 Processing the film and

techniques to bring out

detail in printing 93

4.7 Photography through

coloured filters 95

4.8 Further reading 97

5 Moonshine and chips 99

5.1 Some basic principles of

CCD astrocameras 100

5.2 CCD astrocameras in

practice 102

5.3 Videoing the Moon 106

5.4 Image processing 117

5.5 Getting hard copy 118

5.6 Some CCD equipment

suppliers 124

6 The physical Moon 125

6.1 The first lunar scouts 125

6.2 Men on the Moon 128

6.3 The post-Apollo Moon 132

6.4 Not green cheese but . . . 133

6.5 Genesis of the Moon 134

6.6 The Moon’s structure 135

v

CONTENTS

6.7 The evolution of the

Moon – a brief overview 137

6.8 Lunar chronology 139

6.9 Filling in the details 140

7 The desktop Moon 145

7.1 The Lunar Sourcebook 145

7.2 Spacecraft imagery 146

7.3 The Internet 146

7.4 Lunar ephemerides 147

7.5 Measuring lunar surface

heights 147

7.6 Maps, globes, posters and

charts 150

7.7 Key map for Chapter 8 151

8 ‘A to Z’ of selected lunar

landscapes 155

8.1 Agarum, Promontorium 156

8.2 Albategnius 159

8.3 Alpes, Vallis 159

8.4 Alphonsus 161

8.5 Apenninus, Montes 164

8.6 Ariadaeus, Rima 168

8.7 Aristarchus 171

8.8 Aristoteles 177

8.9 Bailly 179

8.10 Bullialdus 181

8.11 Cassini 184

8.12 Clavius 187

8.13 Copernicus 190

8.14 Crisium, Mare 198

8.15 Endymion 204

8.16 Fra Mauro 208

8.17 Furnerius 213

8.18 ‘Gruithuisen’s lunar

city’ 219

8.19 Harbinger, Montes 222

8.20 Hevelius 225

8.21 Hortensius 232

8.22 Humorum, Mare 235

8.23 Hyginus, Rima 243

8.24 Imbrium, Mare 246

8.25 Janssen 256

8.26 Langrenus 260

8.27 Maestlin R 265

8.28 Messier 267

8.29 Moretus 269

8.30 Nectaris, Mare 271

8.31 Neper 276

8.32 Pitatus 279

8.33 Plato 283

8.34 Plinius 290

8.35 Posidonius 296

8.36 Pythagoras 299

8.37 Ramsden 302

8.38 Regiomontanus 306

8.39 Russell 311

8.40 Schickard 316

8.41 Schiller 320

8.42 Sirsalis, Rimae 324

8.43 “Straight Wall”

8.43 (Rupes Recta) 329

8.44 Theophilus 332

8.45 Torricelli 337

8.46 Tycho 339

8.47 Wargentin 346

8.48 Wichmann 349

9 TLP or not TLP? 353

9.1 The mystery unfolds 353

9.2 Categories of TLP 358

9.3 The mystery continues 359

9.4 What might be the

cause(s) of TLP? 368

9.5 Possible causes of bogus

TLP 370

9.6 TLP observing

programme 373

Index 375

vi CONTENTS

PREFACE

Interest in the Moon periodically ebbs and flows, like the tides it causes in

our oceans. The years leading up to the Apollo manned landings marked a

particularly high tide. Since then there has been a very deep low tide – but

the tide is turning once again. Recently we have had the Clementine and

Lunar Prospector probes and professional studies of the Moon are on the

increase. It is not unreasonable to expect that within the next two or three

decades people will be walking once again on the eerie lunar surface.

When it does happen we will be back to stay this time.

We already know a great deal about our Moon but many mysteries

remain. A few of these mysteries might be solved by the modern-day back-

yard observer. Nonetheless, there are many other motives for the amateur

devoting time and energy to study the Moon, or any of the other celestial

bodies, through his/her telescope, aside from any wish to do cutting-edge

science. I will not waste space listing the other possible motives here. All

that really matters is that you, the reader of this book, have an interest in

the Moon which you wish to explore. If so, then this is the book for you!

I intend this book to be a ‘primer’, a guide for the interested amateur

astronomer who is yet to become a lunar specialist. Of course I have pro-

vided details about practical matters, such as equipment and techniques,

but I have also included a limited amount of the history of the study of the

Moon and, particularly, of lunar science. Without the science (and to a less

important extent, the history) the subject would be sterile and any practi-

cal work beyond simple sight-seeing would be pointless.

To ‘shoehorn’ everything I needed to say into the book-length available

has not been easy. The facts of commercial life apply to books as to any

other commodity. This book is highly illustrated and was expensive to

produce because of this. To keep the cost to you from becoming astronom-

ical in every sense of the word, I have had to keep its length to within very

tight limits set by the publisher. Consequently, time and time again I have

had to refer you, the reader, to other publications to expand on points that

I had not room enough to adequately cover in this book.

However, that shortcoming is also a strength. As I said, this book is a

‘primer’. It is certainly not intended to be the definitive history of lunar

studies, nor of our scientific understanding of the Moon. I can’t really say

that it is the last word on practical techniques and equipment for the

vii

practising amateur astronomer, either. What I can claim for this book is

that it contains enough working knowledge to give any tyro lunar observer

a flying start. Beyond that, this book is intended to be a ‘springboard’ to

further studies and practical work. Please do follow up the references I give.

Go beyond that and seek further ones on your own. Your knowledge of the

Moon and how it has been studied will expand beyond any limits set by the

finite size of any one single-volume work.

I hope you like this book and find it interesting. Much more impor-

tantly, I hope that you discover for yourself the thrills of examining the

Moon’s mountains, craters and other surface structures through your tele-

scope’s eyepiece. Aside from the awesome spectacle of the views, you will

find real fascination in understanding how the Moon got to be as it is.

Gerald North

Bexhill on Sea

viii PREFACE

ACKNOWLEDGEMENTS

I am very grateful to the following people for allowing me to reproduce

examples of their work in this book: Terry Platt, Gordon Rogers, Tony Pacey,

Nigel Longshaw, Andrew Johnson, Roy Bridge, Cmdr. Henry Hatfield, and

Martin Mobberley. Special thanks are also due to Dr T. W. Rackham and

Manchester University, England, to Professor E. A. Whitaker and the Lunar

and Planetary Laboratory, University of Arizona, USA, and to the National

Aeronautics & Space Administration (NASA) for allowing me to reproduce

many of their excellent photographs. Full acknowledgements are given in

the captions accompanying the illustrations within this book. In addition,

Mr John Hill has freely given of his advice on matters involving computers

and the Internet and has gone to considerable trouble to furnish me with

materials. To all these people I am very deeply grateful.

Gerald North

Bexhill on Sea

ix

“Magnificent desolation”

Feverishly excited, I sat cross-legged in front of the family television set and

watched the fuzzy, indistinct, shapes of Neil Armstrong and Buzz Aldrin

moving about amid the grey wash that was the surface of the Moon. The

fact that the picture was of poor quality because it had been beamed back

to Earth through a quarter of a million miles of space did little to dampen

my enthusiasm. I could also make out part of the spidery form of their

space vehicle extending from the grey wash into the black stripe that rep-

resented the airless sky over the Moon. The sound quality was also poor.

The words of those first men on the Moon sounded crackly and wheezy and

so were often difficult to decipher. Nonetheless I listened hard. I may well

have been a mere boy at the time but my sense of the significance of what

I was witnessing was intense. I heard Neil Armstrong’s words before he

stepped onto the lunar soil. I heard Buzz Aldrin describe the scenery

around him as “magnificent desolation”. I wished I was there with them to

see it.

I was born just after the beginning of what used to be called ‘the Space

Age’. As far back as I can remember I have been interested in things scien-

tific and technical and have been infected with a particular passion for

matters astronomical. I avidly read books about science and astronomy. By

the time of that first Moon landing I had acquired an old pair of binoculars

and had been bought a very small terrestrial telescope. Whenever I was

allowed to go outside after dark I turned these humble instruments

towards the Moon and gazed at the dark patches and the craters that they

imperfectly revealed. The proper astronomical telescope I yearned for was

at that time beyond my means.

It is difficult for those who were not around at the time to imagine the

feverish excitement and air of expectation that gradually built up through

the 1960s as the world’s space agencies rapidly made the advances towards

1

No, not a still from ascience-fiction movie but areal (Apollo 17) astronaut bythe ‘Station 6 Boulder’ onthe North Massif of theMoon’s Taurus–LittrowValley! The South Massifcan be seen on the far sideof the Valley. The Apollo 17mission in December 1972was the last manned expe-dition to the Moon’sairless surface. (NASAphotograph.)

CHAPTER 1

that first manned Moon landing. As well as a huge variety of merchandis-

ing such as books, booklets, posters, and kits to make plastic models of

various rockets, television companies enthusiastically broadcast news

items and informative programmes about the ‘space race’. Our television

screens were also awash with many science-fiction shows – Doctor Who and

Space Patrol (called Planet Patrol in the USA) being particular favourites of

mine – that featured space travel to other worlds. The fantasy shows

reflected the public’s yearning for real astronauts to travel through space

and walk on real alien worlds. I very much shared that yearning.

The next few years brought further advances and more space missions.

The pictures and sound got clearer. The Christmas of 1970 was significant

for me in that my parents bought me a ‘proper’ astronomical telescope. It

was a 3-inch (76 mm) Newtonian reflector. Yes, it was still smaller than the

size of instrument recommended for useful work but I shall never forget

the thrill of turning it to the Moon for the first time and seeing the large

iron-grey lunar ‘seas’ and the rugged mountain ranges and magnificent

craters come into sharp focus.

A few years were to pass before I was able to graduate to more powerful

telescopes. I was to spend many hours ‘learning my craft’ at the eyepiece of

that first ‘proper’ one. I didn’t know it then but observing the Moon

through telescopes was to become an important part of my life. After grad-

uating in astronomy and physics, I was even to spend several years as a

guest observer of the Royal Greenwich Observatory and so get to use pro-

fessional telescopes to carry out, amongst other projects, lunar research.

I must have spent several thousands of hours of telescope time observing

the Moon. You might have thought that I would be tired of it by now.

Absolutely not! I hope to show you why not in the pages of this book. I hope

that you, like me, will be thrilled anew every time you view the spectacle

of our neighbouring world’s “magnificent desolation”.

1.1 AN ORBITING ROCK-BALL

Even today there are people (amazingly, even some in our western society)

who are unaware of the Moon’s true nature and status. I should hope that

this does not apply to any of the readers of this book. However please let

me, for completeness if for no other reason, state some of the basic facts.

The Moon is a solid, rocky, body with an equatorial diameter of 3476 km. It

orbits the Earth at a mean distance of 384 000 km. Though often appear-

ing brilliant in the night sky, the Moon does not emit any light of its own

generation. It shines purely by reflected sunlight (and a small amount of

fluorescence caused by the re-radiation at visible wavelengths of invisible

short-wave solar radiations and absorbed kinetic energy from solar-wind

bombardment).

2 “MAGNIFICENT DESOLATION”

The Moon’s diameter is over a quarter of that of the Earth (12756 km

for comparison) and this has led many to consider the Earth and Moon as

a double-planet system, rather than as a true parent planet (the Earth) and

attendant satellite (the Moon). Certainly the statement that “the Moon

orbits the Earth” is an approximate one. In truth both orbit their barycen-

tre, or common centre of mass. For two co-orbiting bodies of equal mass the

centre of mass of the system lies exactly half-way between their centres (see

Figure 1.1(a)). In the case of one body being more massive than the other,

the barycentre is still in mid-space but is shifted towards the more massive

body. In fact the ratio of the distances from each body to the barycentre

is in the inverse ratio of their masses. This point is illustrated by Figure

1.1(b) and 1.1(c). In the case of the Earth and Moon, the Moon’s mass is

7.35�1022 kg and that of the Earth is 5.98�1024 kg (81 times more massive).

This results in the ratio of the distances from the centre of the Moon to the

barycentre and from the centre of the Earth to the barycentre being 81:1.

Put another way, the barycentre lies 1/82 of the way along a line joining the

centre of the Earth to the centre of the Moon. 1/82 of 384 000 km is a little

under 4700 km and so the barycentre lies inside the Earth’s globe. The

Earth may ‘wobble’ as the Moon orbits but the statement about the Moon

orbiting the Earth is approximately true and I, at least, think that this fact

qualifies the Moon as the Earth’s satellite rather than them both being

regarded as a double planet.

1.1 AN ORBITING ROCK-BALL 3

Figure 1.1 The positions ofthe barycentre for bodiesof differing masses. Thedistances of each of thebarycentres from thebodies are in the inverseratios of their masses ineach of these cases.

1.2 PHASES AND ECLIPSES

Nowadays most people are aware that the Sun acts as the central hub of our

Solar System and that the planets orbit at various distances from it. I have

detailed elsewhere the story of how the ancients came to realise this

(Astronomy Explained, published by Springer–Verlag in 1997) but suffice it to

say here that the researches of Copernicus and Galileo at the end of the six-

teenth and beginning of the seventeenth centuries were pivotal. Of course,

one body was not displaced from its location of orbiting the Earth, as the

ancients had previously believed was the case for all the bodies of the Solar

System: the Moon.

The Moon’s sidereal period, the time it takes to complete one circuit of

the Earth, is 27.3 days. At the beginning of the seventeenth century

Johannes Kepler had determined that the orbits of the planets about the

Sun were elliptical, rather than being circular in form as had been thought

by Copernicus. The Moon’s orbit is also elliptical. At the point of closest

approach, perigee, the Moon’s distance is 356410 km. This increases to

406679 km at apogee.

Figure 1.2 provides the usual elementary explanation of how the Moon’s

phases are produced over a complete cycle, or lunation. What the diagram

does not reveal is why it is that the length of the cycle is not 27.3 days, the

same as the sidereal period. The reason is that while the Moon is making its

circuit of the Earth, the Earth itself is moving along its own orbit around the

Sun. Hence the direction of the sunlight changes a little with time, instead

of being fixed as implied in the diagram. Consequently, the Moon has to go

a little further than one circuit round the Earth to go from one new Moon

to the next. So, the length of a lunation, or synodic period is 29.5 days.

As well as the phases, Earthshine, often called “the old Moon in the New

Moon’s arms” is another commonly recognised phenomenon. Figure 1.3

shows it well. Most obvious to the naked eye when the Moon is little more

than a thin crescent but seen more often with optical aid, this is caused by

reflected light from the Earth shining on the Earth-facing part of the Moon

experiencing night. Leonardo da Vinci is credited as being first to correctly

explain this effect. In part, the Earthshine is easiest to see when the Moon’s

crescent is thin because there is not so much glare from the sunlit portion.

Also, when the Moon appears as a crescent from the Earth, the Earth

appears gibbous from the surface of the Moon. One could say that the

apparent phase of the Earth as seen from the Moon is the opposite of that

of the Moon seen from the Earth. So, when the Moon’s crescent is thin the

amount of reflected light from the Earth shining on the Moon is nearly at

its maximum. Apart from the foregoing, the apparent brightness of the

Earthshine also depends on the amount of cloud cover in the Earth’s

atmosphere (as seen from the surface of the Moon, the Earth would appear


at its most brilliant when largely covered in highly reflective clouds).

Finally, the observing conditions local to the observer also have an impor-

tant bearing. Poor transparency and haze both inhibit the visibility of

Earthshine, just as one would expect.

Another way that Figure 1.2 is inaccurate is in that it does not reveal the

true three-dimensional relationship between the Earth, the Moon and the

Sun. Realising that the Earth casts a huge cone-shaped shadow into space,

one might imagine that every full Moon our satellite ought to pass into this

shadow cone (see Figure 1.4). Of course such, lunar eclipses do occur but cer-

tainly not at the time of every full Moon. Neither do solar eclipses occur at

1.2 PHASES AND ECLIPSES 5

Figure 1.2 The phases ofthe Moon. The uppersection of the diagramillustrates the Moon invarious positions in itsorbit, while the corre-sponding phases that wesee from the surface of theEarth are shown in thelower section.

every new Moon (Figure 1.5), even though the diagram might suggest that

the Moon should pass exactly between the Sun and the Earth at these

times. What the diagram does not show is that the plane of the Moon’s

orbit about the Earth is inclined slightly (actually by about 5°) to the plane

of the Earth’s orbit about the Sun.


Figure 1.3 Earthshine.(a) Photographed by theauthor with an ordinarycamera fitted with a58 mm f/2 lens on 3MColourslide 1000 film.

(a)

A useful concept in astronomy is that of the celestial sphere. In this the

sky that surrounds the Earth is represented as the inner surface of a

sphere, the Earth itself being a tiny dot at the centre of the sphere. All the

stars, celestial bodies and the paths along which any of the celestial bodies

appear to move can be shown as projections onto this imaginary sphere.

Figure 1.6 shows such a celestial sphere on which is projected the monthly

orbit of the Moon. Also shown is the yearly apparent path of the Sun across


Figure 1.3 (cont.)(b) A close-up, photo-graphed by Tony Pacey on1993 March 26d 19h 35m UT,using his 305 mm f/5.4Newtonian reflector. Thesunlit portion of the Moonis heavily overexposed inthis 12 second exposure onIlford FP4 film.

(b)

the sky, which results from our orbit around the Sun (in effect the Sun

appears to move once around the sky, through the constellations of the

Zodiac, taking one year to complete one circuit). The Sun’s annual path

across the sky is known as the ecliptic.

The different inclinations of the Moon and Earth’s orbital planes are

reflected in the inclinations of the ecliptic and the Moon’s path on the

celestial sphere. Note how the Moon’s path and the ecliptic cross at two

diametrically opposite points on the celestial sphere. Where the Moon

crosses the ecliptic going from north to south it is said to be at its descend-

ing node. Crossing south to north, it is then at its ascending node.

Notice how the only times the Moon and the Sun can appear exactly

together in the sky (put another way, both be in the same direction as seen

from Earth) are when both are at either the ascending node or both at the

descending node at the same instant. Remembering that the condition for

eclipses to occur is that the Earth, Sun and the Moon must simultaneously

lie along the same straight line at the time of full Moon (for a lunar eclipse)

or new Moon (for a solar eclipse), it is not hard to see why eclipses are rela-

tively rare. For the vast majority of lunations new Moons occur with the

Moon appearing just a little north or just a little south of the Sun in the

sky. Similarly, the Moon manages to miss the Earth’s shadow cone, passing

either north or south of it, at the time of most full Moons.

The situation shown in Figure 1.4, very much out of scale for the sake

of clarity, is that for a total lunar eclipse, where the Earth passes through the

full shadow, or umbra. First the Moon enters the partial shadow, or penum-

bra. The dimming of the full Moon is only very slight at that time. As the

Moon enters the umbra so a ‘bite’ begins to appear and the direct sunlight

is progressively cut off. For a typical total lunar eclipse it will take about an

hour for the Earth’s shadow to completely sweep across the Moon’s surface

(see Figure 1.7). Then all the direct sunlight will be cut off. The only light

reaching the surface of the Moon then is that refracted and scattered by

the Earth’s atmosphere. Usually the Moon then looks very strange, bathed

as it then is by a copper-coloured glow. For an eclipse of maximum dura-


Figure 1.4 Lunar eclipses.With the Moon (black disk)in the position shown, atotal lunar eclipse wouldbe the result. This diagramis grossly out of scale forthe sake of clarity.

tion, totality lasts about an hour and then the umbral shadow leaves the

Moon over the course of another hour, or so.

How much dimming there is, and the precise colourations seen, vary

from eclipse to eclipse (and can even vary during the course of an eclipse).

Also, the size of the Earth’s umbral shadow can vary a little from eclipse to

eclipse, so altering the precise timings and the durations of the eclipses.

There is no mystery about these variations. They reflect the state of the

Earth’s atmosphere at the time of each of the eclipses.

Actually, it might be that for a particular eclipse the Moon is not close

enough to its orbital node and may only partially enter the umbral shadow.

In that case a partial lunar eclipse results. If the Moon misses the umbra alto-

gether, the result is then termed a penumbral eclipse, though most casual

observers will be hard-pressed to spot the very slight dimming that results.

On average, about two lunar eclipses are visible each year from somewhere

on the Earth’s surface.


Figure 1.5 Solar eclipses.(a) An observer stationed atb would see a total solareclipse, while someone inthe regions shown as awould see a partial eclipse.(b) An observer at positionx would see an annulareclipse. The diagrams aregrossly out of scale for thesake of clarity.

Observing lunar eclipsesGiven that eclipses vary from one to another, there is some real scientific

value in observing them, even though the changes are due to differing

geometry and the state of the Earth’s atmosphere and not due to any

change on the Moon. Moreover, the observations can be made using the

naked eye, binoculars, or telescopes. Images of the Moon can be recorded

by means of drawings, photography, video cameras or CCD astrocameras.

You will find information about all of these techniques in the relevant

chapters of this book.

The darkness of a lunar eclipse can be rated using the Danjon scale. A

Danjon 0 eclipse is the darkest. At mid-totality the Moon is almost invisible.

A Danjon 1 eclipse is very dark, with a deep-brown or grey umbra, and

surface details on the Moon are difficult to make out. A Danjon 2 eclipse is

usually deep red, or reddish brown in colour, though near the edge of the

umbra the Moon can look bright orange. A Danjon 3 eclipse is brighter still,

though the umbra still looks coppery red and its edge is often coloured

bright yellow. A Danjon 4 eclipse is the brightest, with the Moon looking

bright orange or even yellow at mid-totality.


Figure 1.6 The orbit of theMoon projected onto thecelestial sphere.

Contact times of the leading and departing edges of the umbra with the

east and west limbs of the Moon and with particular lunar features are of

interest, as are descriptions (best of all with photographs/images) of the

appearances of the umbra (and any penumbral dimming) and the appear-

ances of particular lunar features at stages during the progress of the

eclipse. You might like to make a special search for any unusual appear-

ances. The controversial subject of transient lunar phenomena (TLP) is

covered in Chapter 9 of this book.

Perhaps I should emphasise that Figure 1.5, which illustrates how solar

eclipses are formed, is also grossly out of scale for the sake of clarity. It has

always struck me as a remarkable coincidence that the Sun and the Moon

both appear to be virtually the same apparent size as viewed from the

surface of the Earth. This is approximately 1⁄2° – roughly equivalent to a

span of a centimetre as seen from a distance of 1 metre. It just so happens

that the ratio of the actual diameter of the Sun to its distance from us is

almost equal to that of the diameter of the Moon to its distance from us.

As Figure 1.5 illustrates a total solar eclipse can only been seen from a

restricted region on the Earth’s surface at any given moment. In fact, owing

to the Earth’s rotation and the relative motions of the Earth and Moon (and


Figure 1.7 The lunar eclipse of 1996 April 3d photo-graphed by Martin Mobberley, using his 360 mm reflector(at the f/5 Newtonian focus) on Fuji Reala film. (a) 1/1000second exposure at 22h 25m UT. (b) 1/250 second exposureat 23h 00m UT. (c) 3 second exposure at 23h 20m UT.

(a)

(b) (c)

their relation to the Sun), this small region sweeps across the globe. A

narrow track is generated across the surface of the Earth within which the

eclipse can appear as total. All other regions will see, at best, a partial solar

eclipse (see Figure 1.8).

The maximum duration of totality, as seen from any particular loca-

tion, is about 8 minutes and it varies from eclipse to eclipse. The reason for

the variation lies in the fact that the Earth’s orbit about the Sun is slightly

elliptical, as is the Moon’s orbit around the Earth. Totality will last the


Figure 1.8 The partialsolar eclipse of 1982 July20d, photographed by theauthor with a single-lensreflex camera (fitted with a58 mm lens). 1/500 secondexposures at f/16 on KodakEktachrome 400 film.(a) Exposure at 19h 26m UT.(b) Exposure at 19h 33m UT.

(a)

(b)

longest when an eclipse occurs at a time when the Earth is at its greatest

distance from the Sun, or aphelion, and the Moon is at perigee. In the con-

verse situation, with the Earth at perihelion and the Moon at apogee, the

Moon’s apparent size is actually slightly smaller than that of the Sun. At

maximum eclipse the Sun’s disk will not be completely hidden by the

Moon and a thin ring of sunlight will surround the dark disk of the Moon.

This is an annular eclipse and is illustrated in Figure 1.5(b).

A total solar eclipse is a spectacular thing to see. Over the course of

about an hour a larger and larger ‘bite’ is taken out of the Sun as the

(invisible against the daytime sky) disk of the Moon passes over it. Then

the last sliver of solar photosphere disappears from sight. The sky rapidly

darkens and the Sun’s pearly corona comes into view (see Figure 1.9).

Sometimes solar prominences can be seen over the edge of the Moon. After

just a few minutes the first chink of sunlight peeks once again from

behind the Moon and the sky rapidly brightens and the Moon slowly

withdraws and the eclipse becomes a mere memory for those who

witnessed it.

As the Moon moves around the Earth, the Earth–Moon system moves

around the Sun. Every so often the Earth, Sun and Moon regain very similar

positions relative to one another. This happens every 6585 days (a little over

18 years) and this period has been given the special name of the Saros.

Ancients found the Saros useful in predicting lunar eclipses. A lunar

eclipse happening on a particular day will be followed by one 6585 days


Figure 1.9 Total solareclipse photographed byMartin Mobberley fromChile, 1994 November3d 12h 20m UT. Martin useda Celestron C90 catadioptrictelescope (1000 mm focallength, f/11) for this 2second exposure on FujiVelvia film.

later (of course, that is not to say that other lunar eclipses won’t happen in-

between these times – they will, but each lunar eclipse will be ‘paired’ with

one happening one Saros period later). The Saros is rather less useful in pre-

dicting solar eclipses because it is not quite accurate enough.

1.3 GRAVITY AND THE TIDES

An oft-repeated fable is that Isaac Newton was sitting in his garden one day

and chanced to see an apple fall from a tree. Newton’s genius was such that

he realised that the same force that operated to make the apple fall to the

ground was responsible for keeping the Moon in orbit around the Earth.

He also reasoned that it was quite likely that the same type of force oper-

ates between the planets and the Sun, keeping the Earth and the other

planets in their orbits around our parent star. Whether or not it really was

the falling apple that gave him his inspiration, Newton explored his ideas

mathematically and he published his results in his masterly work, the

Principia, in 1687.

Newton formulated a ‘law’ which he thought would be true for any-

where in the observable Universe:

Any two bodies will attract each other with a force which is proportional tothe product of the masses and is inversely proportional to the square of thedistances separating them.

The law can be expressed in equation form:

F � Mm/r2

or F�GMm/r2 (1.1)

where F is the mutual attractive force, measured in newtons, M, m are the

masses of the attractive masses, measured in kilograms, r is the distance of

separation, measured in metres, and G is a constant of proportionality,

usually known as either the universal constant of gravitation, or the gravita-

tional constant.

Historically, getting a precise value for G was not an easy thing to do but

by modern times a reliable figure has been arrived at by means of sophisti-

cated laboratory experiments. Its value is 6.67�10�11 Nm2 kg�2 . Knowing

the masses of the Earth and the Moon, one can use the equation to work

out the size of the attractive force between them. It amounts to a colossal

2�1020 N. As far as the Earth is concerned, most of this force acts on the

solid part of the body, but a fraction of it acts on the Earth’s fluid covering

and so contributes to the generation of the ocean tides.

The pull of the Moon causes a bulging of the oceans in the direction of

the Moon. In effect, the Earth’s waters are ‘heaped up’ because of the

attraction of the Moon. In addition, the Earth is also ‘pulled away’ from the


water on the reverse side, so leaving a bulge of water on the opposite side

of the Earth, as shown in Figure 1.10. As the Earth turns on its axis so each

position on the Earth experiences two tides per day.

The Sun also contributes its own effect. Though the Sun is very much

more massive than the Moon, it is very much further away and so the

Sun’s tidal force has only about half the magnitude of that of the Moon.

Around the times of new Moon and full Moon, the tidal forces act along

virtually the same straight line and so at these times the tidal amplitude

is greatest, the sea levels rising and falling by the maximum amount. The

situation is illustrated in Figure 1.11 and the tides at these times are

known as spring tides. Near the times of first and last quarter Moon the Sun

and Moon’s tidal pulls are almost at right angles and so the resultant tides

have their minimum amplitudes (see Figure 1.12). These are neap tides.

Local topographic features will have their effects on the tides that

result at any given location (the situation is often quite complicated in bays

and river estuaries, for instance) but the foregoing describes the situation

on the global scale.

1.4 MORE ABOUT THE MOTIONS OF THE MOON – LIBRATION

That the Moon always keeps the same face presented to the Earth is obvious

even to the casual observer and was well known to the ancients. The expla-

nation for this is both obvious and yet fundamental: the Moon rotates on

its axis with the same period that it takes to orbit the Earth. We say that

the Moon has a captured, or synchronous rotation.

However, the careful observer who is armed with some optical aid will

notice that the Moon’s topographic features do not quite remain exactly

1.4 MORE ABOUT THE MOTIONS OF THE MOON – LIBRATION 15

Figure 1.10 The main tidegenerating process.


Figure 1.11 Spring tidesare formed when the pullsof the Moon and Sun arealigned (even if pulling inopposite directions).

Figure 1.12 Neap tides areformed when the pulls ofthe Moon and the Sun areat right angles to eachother.

stationary on the visible disk over a lunation. In fact, the Moon appears to

slightly nod up and down and rock to and fro over each lunar cycle.

Moreover, the nodding and rocking differ slightly from one lunation to the

next. This effect is termed libration.

If it wasn’t for libration we could have mapped only 50 per cent of the

Moon’s surface before the advent of the space age. We were actually able to

map 59 per cent of the Moon, using observations made over a series of

years. Three separate effects operate to create libration: libration in longi-

tude, libration in latitude, and diurnal libration.

Libration in longitude arises because of the elliptical shape of the

Moon’s orbit and the fact that its speed changes with its distance from the

Earth. When the Moon is close to perigee it moves a little faster than when

it is at apogee, the speed changing gradually from one situation to the

other. However, the rotation rate of the Moon on its axis remains constant.

The result is an apparent 7° east–west rotational oscillation of the Moon’s

globe during the course of a lunation. This effect is illustrated in Figure

1.13.


Figure 1.13 Libration inlongitude. The Moon turnsevenly on its axis but theMoon’s speed variesaround its elliptical orbit.Consequently the twomotions are out of step,although the total timetaken for one rotation isthe same as the time takenfor one complete orbit. Theresult is that the Moonappears (as seen from theEarth) to swivel back andforth in an east–west direc-tion over the course of onelunation.

The Moon’s spin axis is not quite perpendicular to the plane of its orbit.

In fact it is canted over at 11⁄2° (by comparison, the inclination of the Earth’s

rotation axis to the perpendicular to the Earth’s own orbital plane is 231⁄2°).

Added to this is the already mentioned 5° inclination of the Moon’s orbit

to the ecliptic (remembering that the ecliptic is, in effect, the projection of

the Earth’s orbital plane onto the celestial sphere). Taken together, these

inclinations mean that we can see, alternately, up to 61⁄2° beyond one pole,

then the other (see Figure 1.14). This is libration in latitude.

Figure 1.15 shows how diurnal libration arises. As the Earth rotates, so

an observer’s viewpoint changes slightly with respect to the Moon. An

Earth-based observer watching the Moon rising above the horizon will be

able to see a little way further around one limb of the Moon, and then a

little further round the other limb when the Moon is setting.

As you might imagine, the way these separate librations combine is

complicated, and is made even more so by the fact that the Earth’s and

the Moon’s orbit precess (the positions of the nodes shift with time).

Consequently, librations differ with each lunation. Figure 1.16 shows well

the effect of libration.


Figure 1.14 Libration inlatitude.

Figure 1.15 Diurnal libra-tion.


Figure 1.16 The effects oflibration are illustratedwell by these photographstaken by CommanderHenry Hatfield, using his12-inch (305 mm)Newtonian reflector:(a) was taken on 1966 May29d 21h 03m UT; (b) wastaken on 1966 November22d 18h 14m UT. In both (a)and (b) the values of thelibration in latitude areclose to their mostextreme possible, thoughall three types of librationmay be variously promi-nent at any given time incombination.

(a)

(b)

1.5 CO-ORDINATES ON THE SURFACE OF THE MOON

Compare a pre-1960s map of the Moon with a modern one and you will

notice that east and west are marked on it the opposite way round. On the

classical scheme the Lunar ‘sea’ (dark area) known as the Mare Crisium was

situated on the western side. This side of the Moon’s face is the east on

modern maps. The modern scheme is due to the International Astronomical

Union (IAU) and is now the accepted standard.

Latitudes and longitudes can be assigned to positions on the Moon’s

globe in the same way that they can on the Earth. Co-ordinates that refer

to the surface of the Moon are known as selenographic. Of course, libration

affects the precise apparent positions of features on the lunar surface but

a co-ordinate system has been derived that refers to the mean apparent

positions – those that would correspond to zero libration.

The mean centre of the Moon’s disk corresponds to a selenographic lati-

tude of 0° and a selenographic longitude also of 0°. Selenographic latitude is

positive going northwards and negative going southwards, being �90° and

�90° at the lunar north and south poles, respectively. Selenographic lon-

gitude increases eastwards (towards the Mare Crisium) and is 90° at the

mean east limb. It further increases (on the part of the Moon turned away

from the Earth) to 180° at the mean position antipodal to the Earth and

round to 270° at the mean west limb. Now on the Earth-facing side again,

the selenographic longitude increases further to 360° (equivalent to 0°) at

the mean centre of the disk.

Figure 1.17 shows an outline map, illustrating the modern co-ordinate

system. Notice that I have orientated it with south uppermost. This is to

make it uniform with the maps and illustrations throughout the book and

is because this book is intended to be of use to the practical observer. Most

readers of this book will live in the Earth’s northern hemisphere and will

see the Moon inverted through a normal astronomical telescope (without

the use of additional optical elements, such as a star diagonal), that is with

this same orientation.

Just as on the Earth, the lines that pass through both poles and the

equator (so forming great circles on the surface of the Moon) are known as

meridians. These are lines of equal longitude. The lines which run parallel

to the equator (so forming small circles over the surface of the Moon – only

the equator is a great circle) are lines of equal latitude.

One can go on to define the co-ordinates of the terminator, the boun-

dary between the sunlit and dark portions of the Moon as the cycle of

lunar phases progresses. The Sun’s selenographic colongitude is the seleno-

graphic longitude of the morning terminator on the Moon. Its value is

270° at new Moon, 0° at first quarter, 90° at full Moon and 180° at last


quarter. In ephemerides it is often reckoned with respect to the mean

centre of the Moon’s disk and so libration can have an effect on the true

position of the terminator on the Moon’s surface. For instance, comparing

a map of the Moon with the ephemeris value of the Sun’s selenographic

colongitude might suggest that the terminator should run through the

middle of a particular feature at a particular time. When you go to the tele-

scope at that time you might find, instead, that libration has carried the

feature rather further into the sunlit portion, or alternately has hidden it

entirely in the Moon’s dark region!

1.5 CO-ORDINATES ON THE SURFACE OF THE MOON 21

Figure 1.17 Outline mapof the Moon, illustratingthe modern system of co-ordinates as standardisedby the InternationalAstronomical Union.

1.6 OCCULTATIONS

As the Moon sweeps around the Earth in its monthly orbit it passes in front

of the planets and stars far beyond. When the Moon hides a more distant

celestial body from our sight we say that it occults that body. A solar eclipse

is an occultation of the Sun. Of course occultations of stars are much more

frequent than solar eclipses.

Though an occultation is usually quite a simple affair, it is really quite

fascinating to watch the edge of the Moon very slowly approach a star until

suddenly the star vanishes from sight. Reappearances are also interesting,

the once hidden star suddenly snapping into view. Of course, one would

normally have to be armed with a prediction that a particular star was

going to emerge at that point and time to be able to catch it happening.

The timings of stellar occultations used to be a valuable pursuit because

it allowed us to derive knowledge of the Moon’s orbit and its surface

profile, as well as precise star positions, amongst many other things. In

modern times some of these objectives have been better met by other

means. However, occultation timings are still useful because the data gen-

erated can be used for certain other investigations. In particular, the long-

term nature of occultation-timing data lends itself to the examination of

the dynamical slowing of the Moon in its orbit. This slowing arises because

of the Moon’s tidal interaction with the Earth.

The binary nature of some stars can be revealed by this technique, even

if they are too close for resolution by more conventional means. Instead of

suddenly snapping out as they pass behind the lunar limb, some stars take

a moment to fade. During a casual observation of an occultation, I found

one star that had not yet found its way to the catalogues as being a binary.

Of course, I reported my find.

In many fields in astronomy it is highly desirable for the observer to

operate as part of a group. I should say that in occultation work it is an

essential requirement. Many provincial societies have observing groups

which collate their results and send them to either of the two main

international occultation organisations. These are the International Lunar

Occultation Centre (ILOC) in Tokyo, and the International Occultation Timing

Association (IOTA) in St Charles, Illinois. In addition to processing observa-

tions, these bodies issue predictions of forthcoming occultations.

As well as the date and expected time of an event, the predictions give

the designation of the star, its magnitude, its co-ordinates (right ascension

and declination), whether the event is a disappearance (immersion) or a

reappearance (emersion). These are obvious essentials for the serious

observer. Another useful piece of data provided is the position angle of the

event. Figure 1.18 shows the path of a hypothetical star behind the Moon

(though one might equally say that the Moon passes in front of the star)


during an occultation. Position angles are measured from the north point of

the lunar disk increasing in an anticlockwise direction. Hence the north

point of the disk has a position angle of zero degrees. The IAU west point (the

classical eastern point) of the disk has a position angle of 90°, and so on.

Occultation timing is one of the decreasing number of projects that

amateur astronomers can still usefully pursue with very modest equip-

ment. Even a 60 mm refractor or 76 mm reflector will do provided the

mounting is not too unsteady (the cheapest ‘department store’ telescopes

may well have mountings which are too tremorous, making these abomi-

nations useless even for timing occultations, let alone the other observing

projects the manufacturers would have us believe we will be able to carry

out by using them).

A very rough formula that links the aperture of a telescope to the mag-

nitude of the faintest star one could see with it is the following:

mv�4.5�4.4 log D (1.2)

where D is the aperture of the telescope in millimetres and mv is the faint-

est stellar magnitude observable. Various other formulae are published but

1.6 OCCULTATIONS 23

Figure 1.18 The path of ahypothetical star behindthe Moon, during an occul-tation. The angles areexaggerated here for thesake of clarity. The posi-tion angle (measured fromthe north point, increas-ing in an anticlockwisedirection) for the star atdisappearance is approxi-mately 110°, while that ofthe reapearance is approxi-mately 260°.

this one is my own, which I have based on the published results of an exten-

sive practical survey carried out by Bradley E. Schaefer, of the NASA –

Goddard Space Flight Centre. Of course, this formula is merely a blanket

guide since there are many factors to be taken into account in making any

prediction of the limiting magnitude a particular observer will attain with

a particular telescope under particular conditions of observation. However,

based as it is on the practical experiences of a large sample of modern-day

telescope users it should be more accurate than other formulae. Table 1.1

provides a selection of predictions of limiting magnitudes for telescopes

with apertures covering the range generally used by occultation observers.

Mind you, this does not mean than one can necessarily expect to suc-

cessfully observe an occultation of, say, a 14m.1 star by using a 6-inch

(152 mm) telescope. The predictions given by the formula are for stars seen

against a very dark sky background. Even if the occultation is by the Moon’s

dark limb and the brightly sunlit portion is out of the field of view, the

light inevitably scattered from the sunlit portion into the sky around the

Moon is sure to have some effect. If the star is occulted by the sunlit limb

then one would be hard-pressed to see the event even if the star was a

couple of magnitudes brighter than the value given by the formula. The

extreme is, of course, an occultation by the full Moon!


Table 1.1. Telescopic limiting stellar magnitudes, computed from the author’s

formula, which was based on a practical survey by Bradley E. Schaefer. Occultation

observers can use these figures as a ‘best case’ guide; for instance an occultation of

a star by the un-illuminated portion of a thin crescent Moon on a night of excellent

clarity. The varying brightness of the Moon will mean that usually stars rather

brighter than indicated here are the dimmest that will be seen close to the lunar

disk. Of course, the figures given here will be several magnitudes over-optimistic for

the case of an occultation of a star by the full Moon on a hazy night!

Telescope aperture Telescope aperture Limiting magnitude

(inches) (mm) mv

6 152 14.1

8 203 14.7

10 254 15.1

12 305 15.4

14 356 15.7

16 408 16.0

18 457 16.2

20 508 16.4

I recommend beginning the setting up of your equipment at least half-

an-hour before the event is predicted. You will need this time to locate the

star (if the event is an immersion) and to make sure that everything is func-

tional. As in other fields, a permanently mounted clock-driven telescope is

a great convenience, though there is some merit in having a portable tele-

scope if one’s sky-access is limited. With a clock-driven telescope one can

simply identify the star (using setting circles and/or a star chart) and then

set it in the centre of the field of view. Then watch the approach of the

Moon’s limb (even a dark limb is usually visible, owing to Earthshine) and

time the star’s disappearance as accurately as you can. If the Moon’s limb

really is invisible (perhaps the sky transparency is rather poor) then all one

can do is to resort to keeping an eye on the clock and only give full atten-

tion to the view through the telescope from about a minute or so before

the predicted time of the event.

If your telescope does not have a clock-drive then you must contrive to

move the telescope just a little before the event, in order that the occulta-

tion will happen with the star reasonably close to the centre of the field of

view. Again, keeping an eye on the clock until a minute before the pre-

dicted time will help, together with an estimate of how much the star will

drift in that minute (gauged from observing the star’s drift in the field of

view in the preceding minutes). Of course, it is only too easy to move the

telescope too close to the time of the occultation and in that way lose the

event!

A clock-drive is especially useful for observing emersions. Ideally the

telescope is set on the star before it first disappears behind the Moon. Both

immersion and emersion can then be timed. Otherwise, a computer-con-

trolled telescope, or one with setting circles, could be used to set on the co-

ordinates of the star given in the prediction if it is not possible to observe

the immersion. One then has to keep a careful watch for the star’s reap-

pearance. The best an observer limited to using simpler equipment can do

is to keep a careful watch on the lunar limb at the predicted position angle

of the star’s emersion.

Grazing occultations are especially interesting. As the name implies, this

is where the star appears to graze the lunar limb and perhaps appears and

disappears several times behind irregularities in the Moon’s limb. In order

to get the most useful work done, a co-ordinated team can be set up across

the predicted track of the graze event. Provided all the timings are accurate

and reliable, the results from the observers can be subsequently used to

generate an accurate profile of the Moon’s limb (though this is now largely

only for personal interest) and a particularly precise fix for the Moon’s posi-

tion at the time of the event (this is still a valuable piece of information). I

can’t emphasise enough that to be of any real use the observer’s timings

1.6 OCCULTATIONS 25

must be accurate. The following notes detail how sufficient accuracy may

be achieved.

1.7 TIMING AND RECORDING OCCULTATIONS

The traditional tools of the occultation observer are, apart from the tele-

scope, his/her eye and a stopwatch. The aim is to record the time of the

event as precisely as possible, ideally to an accuracy of 0.1 second. The first

requirement is that the stopwatch is reliable, accurate, and easy to use.

Beware tiny buttons (as on many digital watches) and an indefinite

start/stop action. The second requirement is a source of accurate time

signals. You could use the telephone time-service. More conveniently, you

might use a radio tuned to whatever station you can receive time signals

on in your area.

To make the timing start the stopwatch at a given time signal (whether

from the telephone service or from the radio) and then, watching through

the telescope, stop the stopwatch at the instant of the event. If the time of

starting the stopwatch is A and the time of stopping it is B, then the time

of the event is A�B. Remember the need for accuracy. Discard the observa-

tion if you fumble the stopwatch or are obviously ‘caught unawares’ and

delay pressing the stopwatch button for a significant and undeterminable

time. You will need to keep alert and have brisk reactions in order to

achieve the desired 0.1 second accuracy.

Some observers have constructed their own electronic chronometers,

which automatically record the time when a button is pressed on a

handset. In theory this should be fine. However, the apparatus must itself

be reliable and highly accurate. Incorrect timings are not merely useless.

They are positively harmful to the analysis. Fortunately one can use radio,

or telephone, time signals in order to check the running and accuracy of

any home-made chronometer. Even if the long-term running of the device

seems good, it is as well to check the device against a time signal shortly

before, and again shortly after, the observing run.

If the chronometer is consistently running a little fast, or a little slow,

then it can still be used. Obviously one then has to interpolate to correct

the time recorded for the event. However, what is not permissible is a chro-

nometer that changes its rate. The occultation observer should take the

chore of keeping all timepieces monitored, or rated, as an important part

of his/her work.

Using a video camera, or a dedicated CCD astrocamera, with the tele-

scope is described in Chapter 5. Suffice it to say here that a video recording

of the occultation can be made using a sensitive video camera or a CCD

astrocamera. If the video machine or the camera has an on-screen ‘sports-

type’ stopwatch then the event can, in theory at least, be timed with better


accuracy than can be done by the traditional eye-and-stopwatch method.

An American video machine operates at 30 pictures (‘frames’) per second

and so the timing could be potentially accurate to 1/30 second. Most other

countries use TV and video systems which utilise 25 frames per second, cor-

responding to a potential accuracy of 1/25 second. As before, it will be nec-

essary to standardise the VCR’s timer against accurate time signals, both

before and after the observation, as well as rating it over a longer period.

Automation is possible if one is lucky enough to have a computer-

operated telescope which one can use with a CCD/video system. After the

initial set-up period the telescope can be left to ‘do its own thing’ while one

is busy with some other activity. The set-up procedure must always include

checking the timer against which the events are recorded. At the end of the

session one extracts the results and closes down the equipment, once again

checking the timer to make sure that it is still in synchronism with the

standard time signals.

Along with the tabulated observations, the observer is responsible for

reporting his/her exact geodetic co-ordinates. These are the latitude, the

longitude, and the height above mean sea level of the location of the

observer’s telescope. A trip to the library may be sufficient to unearth a

large-scale ordinance survey map and so deduce the required information.

You may wonder if you should make any attempt to allow for the inev-

itable delay from seeing an occultation event and actually pressing the

stopwatch button. The answer is no. The ‘raw’ timings you obtain are the

ones you should record. When your observations are processed at IOTA or

ILOC your results will be compared with others and a personal equation

deduced for you. This is the average delay that occurs between the actual

time of the event and when you stop the stopwatch. The only possible

exception to this is if you are a particularly experienced observer and you

have an accurate value for your own personal equation. Your report must

state whether or not a personal equation has been applied to the figures

and, if it has, the magnitude of the correction. An observer’s personal equa-

tion for emersions will be rather greater than that for immersions.

So much for our very brief survey of the Moon as a chunk of rock in orbit

about the Earth. Aside from occultations work and eclipse observations,

most practical amateur astronomers will be more concerned with the

nature and topography of the Moon’s surface. As this is a book for practi-

cal amateur astronomers, most of the rest of it will be devoted to that field

of study.

1.7 TIMING AND RECORDING OCCULTATIONS 27

The moon through the looking glass

Who first looked at the Moon through a telescope? The honest answer is

that we do not know. We cannot even be sure as to when the telescope was

invented, let alone who was first to look at the Moon through one.

Until a few years ago most historians had settled upon 1608 as the prob-

able year of invention of the telescope and a Dutch spectacle maker, Hans

Lippershey, as its probable inventor. Recently, however, evidence for an

earlier invention has come to light. For instance, an Englishman, Thomas

Digges, is thought to have produced a form of telescope sometime around

1555.

What we can be certain of is that Galileo heard of the Dutch telescope

and, with few clues to help him, he did manage to design and build a small

refracting telescope for himself in 1609. Shortly thereafter he built other

slightly better and more powerful versions (though still extremely imper-

fect and lacking in magnification by modern standards) and we know that

he used them to observe the celestial bodies, including the Moon.

Galileo made sketches of the lunar surface. An Englishman, Thomas

Harriott, had managed to obtain a telescope from Europe and also used

it to observe the Moon at about the same time as Galileo. Harriott even

produced what was very probably the first complete map of the Moon’s

Earth-facing side to have been made using optical aid. Despite the imper-

fections of his telescope, Harriott’s map does show features we can recog-

nise today.

You might have expected the coarsest features of the Moon to have been

charted before the invention of the telescope. Undoubtedly they were,

though the earliest ‘map’ produced without optical aid that we know of is

that by William Gilbert. This was published posthumously in 1651, though

it is supposed that he made it in 1600, or at some time close to that date,

approximately three years before his death.

29

CHAPTER 2

Although the very beginnings of lunar study might be shrouded in the

mists of time, all that occurred after Galileo’s era is quite well documented.

The Moon had become a subject for serious scientific study and astronomers

set about mapping its surface features. As telescopes improved in their

power and quality, so successive observers produced better and better maps.

An essential for any cartographic exercise is the standardisation of

nomenclature. Naming systems were devised by Langrenus in 1645 and by

Johannes Hevelius in 1647. As an aside, Hevelius’s maps were notable

because they were the first to take account of, and to represent, the regions

of the Moon that were only shown as a result of libration. Despite this

advance, Hevelius’s system of nomenclature was quickly superseded. Our

modern scheme of naming lunar surface features really stems from that

devised by Giovanni Riccioli. Riccioli was an Italian Jesuit. A pupil of his,

Francesco Grimaldi, had made a telescopic study of the Moon. Riccioli com-

bined Grimaldi’s observations into a map, which was published in 1651.

Before taking our story further, it will benefit us to pause to consider

the appearance of the Moon through a telescope and to get a brief overview

of the modern nomenclature of the main types of surface features revealed

by one of these wonderful devices.

2.1 THE MOON IN FOCUS

Even a casual glance made without any form of optical aid reveals that the

Moon is not a blank, shining disk. Aside from the phases, the Moon’s silvery

orb clearly shows patchy dark markings. These give rise to the “Man in the

Moon” (and the variety of animals and maidens which feature in other folk

lores) effect which is so obvious around the time of the full Moon. Figures

2.1–2.5 show the general appearance of the Moon at successive stages in its

lunation, as it is seen through a normal astronomical telescope stationed

in the Earth’s northern hemisphere – in other words, with south upper-

most. Since this book is intended for the amateur telescopist and since

most of its readers are expected to reside in the northern hemisphere, all

the telescopic views of the Moon in this book are orientated with south at

least approximately uppermost.

The large dark areas are known as maria, Latin for ‘seas’; the singular

form is mare. Thanks to Riccioli, we have such charming names as Mare

Imbrium (Sea of Showers), Mare Serenitatis (Sea of Serenity), and Mare

Tranquillitatis (Sea of Tranquillity) to encounter on the Moon.

In Galileo’s time it was widely believed that the patches on the Moon

actually were seas. Admittedly, a few scholars considered the darker areas

to be the land masses and the rest of the Moon’s globe to be ocean-covered.

Much later the true, arid, nature of the Moon was recognised and the dif-

ference in hue was taken to indicate a difference in chemical composition.

30 THE MOON THROUGH THE LOOKING GLASS

In pre-space-age times the dark plains were termed lunarbase, while the

lighter-hued materials were termed lunarite.

As well as the ‘seas’, we have one ‘ocean’ (oceanus): Oceanus Procellarum

(Ocean of Storms) and several ‘bays’ (sinus for the singular case), such as

Sinus Iridum (Bay of Rainbows). These are the larger dark areas. In addition

there are a number of ‘marshes’ (paludes), such as Palus Somnii (Marsh of

Sleep) and ‘lakes’ (lacus for the singular case), for example Lacus Mortis

2.1 THE MOON IN FOCUS 31

Figure 2.1 The 4-day-oldMoon, photographed byTony Pacey. He used his10-inch (254 mm)Newtonian reflector at itsf/5.5 Newtonian focus todirectly image the Moononto Ilford FP4 film, subse-quently processed inAculux developer. The1/125 second exposure wasmade on 1991 January 19d.The details of the precisetime (from which I couldwork out the value of theSun’s selenographic colon-gitude) was not given.However, I estimate theSun’s selenographic colon-gitude as approximately307° at the time of theexposure.

(Lake of Death). These are the smaller mare-type dark plains. They are all

easily visible to the user of a pair of binoculars. The lunar equivalent of the

Earthly ‘cape’ is the promontorium. An example is the Promontorium

Agarum (Cape Agarum) on the south-eastern (IAU co-ordinates) border of

the Mare Crisium.

You will find a coarse map of some named lunar features presented in

Chapter 7 (p. 152) of this book. In addition, many of the features named in


Figure 2.2 The 6-day-oldMoon photographed byTony Pacey. Same arrange-ment as for Figure 2.1 buthe used a 1/60 secondexposure on Ilford Pan Ffilm, processed in ID11developer. The photographwas taken on 1992 January10d 19h 00m UT, when thevalue of the Sun’s seleno-graphic colongitude was327°.5.

this chapter are discussed in detail in Chapter 8 and images/illustrations

of them under differing lighting conditions are included there.

Of course, the view grows more detailed when a proper astronomical

telescope is used. Even a small telescope reveals a mass of detail and the

sight of the lunar surface in anything larger than a 3- or 4-inch (76 mm or

102 mm) telescope is impressive to say the least. I find that the appearance

of the Moon’s surface through such a telescope, and using a magnification

of the order of �100, reminds me of plaster of Paris. The waterless ‘seas’

and other dark plains appear various shades of steely grey and the rougher,

crater-strewn, ‘highlands’ that make up the rest of the surface seem greyish

white.


Figure 2.3 The 11-day-oldMoon photographed byTony Pacey. This time Tonyused his 12-inch (305 mm)f/5.4 Newtonian reflector,though with the sametechnique as he used toobtain the photographsshown in Figures 2.1 and2.2. The 1/250 second expo-sure was made on IlfordPan F film on 1992 May13d 22h 14m UT, when theSun’s selenographiccolongitude was 40°.0.

When the Moon is close to full (as shown in Figures 2.3, 2.4 and 2.5) its

surface seems dazzlingly bright and covered in bright streaks and spots

and blotches. At these times it is difficult to imagine that the Moon is made

up of relatively dark rock. In fact the Moon’s albedo is 0.07, meaning that it

reflects, on average, 7 per cent of the light falling on it.

Surface features are difficult to make out near full Moon because the

sunlight is pouring onto the lunar surface from almost the same direction

as we are looking from. This means we cannot see the shadows, so we see

very little in the way of the surface relief as a result.

Away from the times when the Moon is full the effect is far less confus-

ing. Shadowing then makes the lunar surface details stand out. This is espe-

cially so close to the terminator, where the sunlight is striking the Moon at

a very shallow angle. This is evident even by comparing the wide-angle (and

hence low-resolution) views shown in Figures 2.1 to 2.5. Notice how the

surface relief along the terminator in Figures 2.1 and 2.2 is virtually invis-

ible in the corresponding positions in Figures 2.3, 2.4 and 2.5.

Under low-angle lighting even the lunar maria are shown to be less

than perfectly smooth. Dorsum, networks of ridges crossing the maria, then

become obvious (see Figure 2.6). Dorsa are ridges occurring elsewhere than

on the lunar maria. They are named after people, for example Dorsa

Andrusov and Dorsum Arduino, but the average lunar observer will not

have occasion to use these names.


Figure 2.4 The 14.7-day-oldMoon photographed byTony Pacey on 1990December 31d 20h 15m UT,when the Sun’s seleno-graphic colongitude was78°.7. He used a 1/1000second exposure. All otherdetails as for Figure 2.1.

If the lunar ‘seas’ are the easiest features to see with the minimum of

optical aid, then the craters must count as the next-most-dominant surface

feature on the Moon. These saucer-shaped depressions range in size from

the smallest resolvable in telescopes (and smaller, down to just a few

metres across, as revealed by the manned landings) to a few that are several

hundred kilometres in diameter. The smaller craters vastly outnumber the

larger ones.

Following the scheme originated by Riccioli, craters are given the

names of famous personalities, most usually astronomers. If it strikes you

that this is potentially a rather contentious system then you are correct!

Over the years many selenographers had taken it upon themselves to

modify the nomenclature assigned by the earlier workers, often putting

their own names and the names of their friends onto their maps. The

result was that a particular crater might have different names on differ-

ent maps. Even more confusing, a particular name might refer to differ-

ent craters on different maps! Fortunately, the system has been

overhauled by the International Astronomical Union in modern times.

Under the IAU-standardised scheme, craters are still named after famous

personalities (with the proviso that the personality is deceased – the only

exception to that being the Apollo astronauts) and most of the older

assigned names have been retained. The IAU nomenclature is most


Figure 2.5 The 16-day-oldMoon photographed byTony Pacey on 1992November 11d 21h 45m UT,when the Sun’s seleno-graphic colongitude was100°.9. The exposure givenwas 1/500 second. Otherdetails as for Figure 2.3.

definitely the one to be adhered to and I would advise caution when using

pre-1975 maps.

When seen close to the terminator, craters are largely filled with deep-

black shadow and give the impression of being very deep holes. In reality

they are rather shallow in comparison to their diameters and can often be

quite difficult to identify when they are seen well away from the termina-

tor. Craters saturate the highland areas of the Moon (see Figure 2.7) but

there is an obvious paucity of larger craters on the maria. An observer using


a typical amateur-sized telescope (around 200 mm aperture) can resolve

craters down to about 1–2 km in size and yet many areas of the maria

appear craterless. Nonetheless, the photographs sent back by close-range

orbiting probes show that even these areas are saturated with small and

very small craters. Where there are recognised chains of small craters,

these are termed catena and are named after the nearest most appropriate

named feature. Catena Abulfeda is one example; a 210 km-long chain of

small craters near the major crater Abulfeda.

Often the floors of large craters are cluttered with smaller craters and

there are many examples of craters breaking into others. In almost all

the cases it is the smaller crater which breaks into the larger. Clavius

(see Section 8.12), Gassendi (Section 8.22), Posidonius (Section 8.35) and

Cavalerius (Section 8.20) are examples of these.

Craters differ in more than their sizes. Some, such as Copernicus, have

elaborately terraced walls. Copernicus (Section 8.13) is also an example of

one of the many craters to have centrally positioned mountain masses.

Other craters, such as Plato (Section 8.33), have their floors flooded with

mare material. Some craters have their walls broken down and are almost

totally immersed in mare material. Some craters have bright interiors,

such as Tycho (see Section 8.46), which is also one of the best examples of

craters which are the source of bright streaks of material, termed rays,

which extend radially from the source crater. Tycho is very easy to see

through a pair of binoculars any time close to full Moon, appearing as a

bright spot in the Moon’s southern highlands. The rays also seem to extend

more than half-way around the Moon’s globe. Figure 2.5 shows them par-

ticularly well. Other craters have relatively dark interiors and no associated

ray systems. All this tells a story and I will have much more to say about

crater morphologies and the evolution of the Moon and its various surface

details later in this book. For now, we will continue our extremely brief

survey of the main types of lunar surface feature and nomenclature.

After the maria and the craters, mountains (generic name mons) and

mountain ranges and groups of peaks (montes) vie for the attention of the

telescope-user. They have been named after their Earthly counterparts, so

one can find the Apennine Mountains (Montes Apenninus – see Section 8.5)

and Carpathian Mountains (Montes Carpatus – close to the crater

Copernicus – see Section 8.13) on the Moon. The lunar highlands are very

rough and hummocky, whereas the maria are much smoother. However,

mountain ranges often border a mare. Isolated peaks also exist, sometimes

actually on a mare. Examples of this type are Mons Piton and Mons Pico

(close to the crater Plato – see Section 8.33), situated on the Mare Imbrium.

Relatively small blister-like swellings on the lunar surface are termed domes

but these are not given specific names and are, instead, identified by their


Figure 2.6 With sunlightilluminating the surface ata low angle even the lunarmaria appear far fromcompletely smooth.Patterns of ridges cross thepart of the Mare Nubiumthat is shown in thisCatalina Observatory pho-tograph. The instrumentused was the observatory’s1.5 m reflector and thephotograph was taken on1966 May 29d 04h 41m UT,when the Sun’s seleno-graphic colongitude was22°.6. (Courtesy ProfessorE. A. Whitaker and theLunar and PlanetaryLaboratory, Arizona.)

proximity to a known major location in the same way as for the crater

chains. The easiest domes to locate are those near the crater Hortensius.

These are described in Section 8.21.

The closest match to an Earthly cliff on the Moon’s surface is an escarp-

ment (a sudden rise in the ground which continues along an approxi-

mately linear, or slowly curved path). The generic name for these features

are rupes, an example being the Altai Scarp (Rupes Altai – see Sections 8.30

and 8.44) on the Moon’s south-eastern quadrant.

As well as the craters and the various raised formations, features sunk


below the Moon’s surface abound. Gorge-like valleys, called vallis, such as

the huge Rheita Valley (Vallis Rheita – see Section 8.25) are at one extreme

of the size range. Much finer (though often longer) sinuous channels,

known as rilles (obsolete spelling rills; in old books you will also find them

often referred to as clefts, particularly so the larger examples), also cross

the lunar terrain. Several are shown in Figure 2.8. As far as naming them

goes, rima is used for single examples and rimae for networks or groups of

rilles. Hence, Rima Hadley and Rimae Arzachel. Many examples are

detailed in Chapter 8. All the rilles and most of the lunar escarpments

and valleys are named after the closest appropriate major feature. The

sole exceptions are: Rupes Altai, Rupes Recta, Vallis Bouvard and Vallis

Schröteri.


Figure 2.7 The crater-satu-rated southern highlandsof the Moon, photo-graphed using the 1.5 mreflector of the CatalinaObservatory, Arizona,on 1966 September5d 11h 30m UT, when theSun’s selenographiccolongitude was 155°.5.(Courtesy Professor E. A.Whitaker and the Lunarand Planetary Laboratory,Arizona.)

Figure 2.8 Systems of rillessituated near the centre ofthe Earth-facing hemi-sphere of the Moon.Photograph taken usingthe 74-inch (1.9 m)reflector at Kottamia,Egypt, on 1965 August4d 20h 43m UT. (Courtesy DrT. W. Rackham.)

All the foregoing described features can be seen through small tele-

scopes. Even a humble 3-inch (76 mm) refractor is sufficient to show many

rilles, despite their being hard to resolve due to their thinness, when they

are seen under low-angle illumination from the Sun (and so largely filled

with black shadow). They were first noted by Christian Huygens with the

primitive telescopes of the seventeenth century.

As I indicated earlier, the Moon appears rather monochrome when seen

with a small telescope (aside from the prismatic splitting of light through

our atmosphere which causes images seen in a telescope often to be spoiled

by colour fringing – discussed later in this book). However, if a sufficient

aperture is used then some coloured tints can become visible to the

observer. Or at least that is the case for many observers. Sensitivity to

colours varies enormously from person to person. Some observers fail to

see colour in anything they look at through the telescope. For a few lucky

individuals the Universe is a very colourful place. Others can see some

colours through the telescope eyepiece, perhaps just the strongest hues on

Jupiter and the overall colours of Mars and Saturn.

I am fairly fortunate in that I can easily see colours in many objects

through a telescope of sufficient size, though I must say that I have noticed

some reduction in my colour-sensitivity as I have got older. I find that I can

see subtle coloured tints on the Moon’s surface when using a sufficiently

low magnification on a reasonably large telescope; for example, �144 on my

181⁄4-inch (0.46 m) Newtonian reflector. The overall colour of the rough high-

lands are still greyish, though perhaps a little ‘creamier’ in colour than

through a smaller telescope, but the large plain of the maria seem tinted

with faint blues and greens. In particular, the Mare Tranquillitatis seems

especially blue when seen near full Moon. The interiors of some craters,

such as Langrenus, appear with a faint brownish or even a golden-yellow

tint at these times. Aristarchus appears slightly bluish-white while the

raised plateau on which it stands seems particularly brownish to my eyes.

Of course, these colours are very far from accurate. Spectroscopic anal-

ysis reveals that the surface of the Moon is really various shades of brown.

The human eye has a tendency to normalise the overall colour of the Moon

as white. Hence the different shades of brown manifest as the apparent

colours seen. A slightly ‘redder’ brown produces an apparent yellowish or

brownish tint, while a ‘cooler’ shade of brown seems to the observer to be

a greenish or bluish tint.

Figure 2.9 shows a specially prepared photograph on which all the

usual grey-scale tones have been obliterated. Instead, the shades of grey

represent colour differences. Redder tones show up as lighter, and bluer

tones show up as darker. Note the relative blueness of the maria and the

relative redness of the interiors of many craters. As far as I can ascertain


only a minority of people can perceive these subtle tints through even a

large telescope. To most users of small telescopes, the Moon is a world of

black and white, and steely greys.

2.2 THE PIONEERING SELENOGRAPHERS

As the seventeenth century progressed so refracting telescope object glasses

were made which were a little larger than the first, tiny, examples. However,

these lenses were single pieces of glass and so suffered badly from chro-

matic aberration. The remedy for this aberration (and to an extent the other

aberrations that arose mainly from the crudeness of the methods of lens

manufacture) was to make the lens of larger focal ratio (and hence greater

focal length). To reduce the aberrations to a tolerable level, the focal length

had to increase out of proportion to the aperture. So, longer and longer

refracting telescopes were made. In some cases the focal lengths reached

hundreds of feet (several tens of metres). Even then, the sizes of the objec-

tive lenses were still less than 9 inches (23 cm)! Despite this handicap, sele-

nography, the charting of the Moon’s surface features, steadily improved.

2.2 THE PIONEERING SELENOGRAPHERS 41

Figure 2.9 Colour-differ-ence (610 nm – 370 nm).photograph of the MoonThe normal grey-scale hasbeen eliminated. Lighterregions are redder anddarker regions are bluer.

Probably the best map of the Moon made in the seventeenth century

was that published in 1680 by Cassini. His 54 cm map (54 cm representing

the Moon’s diameter), is of remarkable quality considering the cumber-

some telescopes he had to work with. Not only is it artistically a fine piece

of work but also the positional accuracy of the features it depicts is very

good for the time (admittedly it is hardly up to modern standards in this

respect!). It showed unprecedented fine details, such as the minute craters

(which we now know as secondary craters) around Copernicus. It is also more

comprehensive in its depiction of features than earlier works, for instance

showing the ray systems that surround many bright craters (de Rheita was,

arguably, the first to comprehensively chart the rays in 1645) and some-

thing of the variations of hue of the lunar maria.

The later years of the seventeenth century also saw the invention of the

common forms of reflecting telescope (the Newtonian, the Cassegrain and

the now obsolete Gregorian) which eventually led to more manageable and

yet higher-quality instruments, and ever better lunar observations.

In Germany Tobias Mayer produced a small, though accurate, map, pub-

lished posthumously in 1775. He was notable in that he was the first to

introduce a system of co-ordinates for lunar surface features, having made

his measurements with the aid of a primitive eyepiece micrometer.

As far as the ‘leading lights’ of selenography go, Germans dominated

the period from Tobias Mayer’s work through to the late nineteenth

century. Perhaps the most famous of these was Johann Hieronymous

Schröter. Schröter was a magistrate at Lilienthal (near Bremen, in

Germany), where he had enough wealth and leisure time to set up his own

observatory. He had various telescopes, including two by William Herschel.

His largest (not by Herschel) was a 20-inch (0.51 m) Newtonian reflector of

about 8 metres focal length. Completed in 1793, it was the largest telescope

in Europe at the time and was surpassed only by William Herschel’s 48-

inch (1.2 m) of 40 feet (12 m) focal length, though it is thought that the

optical quality of the 20-inch was not particularly good.

From 1778 to 1813, Schröter devoted considerable amounts of time and

energy to observing the Moon and planets. He set himself the task of making

the most detailed map of the Moon to date and he made hundreds of lunar

drawings to that end. He used a crude eyepiece micrometer to aid his work,

including making measurements of the heights of lunar mountains. He was

the first to make a really detailed study of the crack-like rilles. In the end he

did not complete his proposed lunar map but instead published the com-

pleted sections in a book, Selenotopographische Fragmente, in 1791 (a second part

was completed and a bound two-volume edition published in 1802). Schröter’s

work attracted much attention and other selenographers undoubtedly were

inspired by the (sometimes controversial) results issuing from Lilienthal.


On the downside, Schröter was not a particularly good draughtsman

and he certainly made his fair share of mistakes. In particular he thought

he had detected changes on the lunar surface over the years during which

he carried out his observations and he was convinced that the Moon pos-

sessed a dense atmosphere. Of course, neither are true.

A cruel blow was to befall Schröter when, in April 1813, invading French

soldiers looted and then burnt Lilienthal to the ground. His observatory

was also looted and then destroyed. At that time Schröter was 67 years old

and his health was already in decline. It was too late for him to rebuild his

observatory and begin again. Undoubtedly the shock and sorrow he suf-

fered hastened his death. He died three years later.

Wilhelm Lohrmann, of Dresden, also attempted to map the entire face

of the Moon in great detail. The first sections of his map were published in

1824 but Lohrmann was eventually defeated by failing eyesight. However,

he did manage a general map of the surface of 39 cm diameter. The quest

was taken up by Wilhelm Beer and his collaborator Johann Mädler. Beer

had a 33⁄4-inch (95 mm) refractor at Berlin and, together, they used this tele-

scope to study the Moon in detail for over a decade. They eventually (1837)

produced a highly detailed and very accurate map. On it, the whole Moon

had a diameter of just over 0.9 m. It remained unsurpassed for decades to

follow, a significant achievement given the diminutive size of the telescope

they used. Beer and Mädler’s map was supplemented with their book Der

Mond. They portrayed the Moon as utterly dead and changeless, in complete

contrast to the picture of it painted by Schröter.

Whereas the Moon of Schröter, with its supposed changes and active

weather tended to excite the interest of others, that portrayed by Beer and

Mädler tended to do the opposite. Given, also, the high quality of their

map, the general feeling was that ‘the last word’ had been stated as regards

lunar studies. Few others studied the Moon seriously for more than the

next quarter-century.

However, one exception was Julius Schmidt. Schmidt had a lifelong

interest in the Moon. After posts at various German observatories, he

became Director of the Athens Observatory, in Greece, in 1858. He used the

7-inch (178 mm) refracting telescope there to continue his lunar studies. As

well as revising the sections of the lunar maps of Lohrmann, and then

going on to complete the mapping of the missing sections, Schmidt was

eventually to complete one of his own by 1878.

Schmidt’s map, 1.9 m to the Moon’s diameter (the map was divided into

25 sections) was incredibly detailed as well as being reasonably accurate. It

recorded and placed some 32 856 individual features. It took over the torch

from Beer and Mädler as the best lunar map. It was to hold this premier

position until 1910, when a 1.5 m map of greater positional accuracy was


published by Walter Goodacre, the second Director of the Lunar Section of

the British Astronomical Association (BAA).

This was not Schmidt’s only contribution to selenography. Owing to an

erroneous interpretation of his, and other people’s, observations, he re-

invigorated lunar research. The whole episode concerns a small crater,

called Linné, in the Mare Serenitatis. Lohrmann, Beer and Mädler, and

Schmidt himself had often recorded Linné as a deep crater. Then, in 1866,

Schmidt announced that the crater had disappeared! In its place Schmidt

could only find a small light patch. As one might expect, a statement like

that was sure to get astronomers turning their telescopes back to the Moon.

Many leading astronomers joined in and a vigorous debate ensued. In fact,

many astronomers continued to cite Linné as a prime example of an area

of the Moon that had changed significantly within the history of Man’s

observations of it, even to as late as the middle of the twentieth century!

We now know that Linné is really a small crater surrounded by a light

area. Under certain angles of illumination it can, indeed, appear in the

guise of a deep, apparently larger, crater. It seems certain that Schmidt

was mistaken. There never was any change in this lunar feature within the

period when astronomers were looking at it. However, this mistake was

just what was needed at the time to counter the view of the Moon as a dead

and uninteresting world that pervaded after Beer and Mädler’s epic study

of it.

As well as the maps, various other studies of the Moon’s topography

appeared in the form of books. For instance, there was The Moon jointly

authored by James Nasmyth (a famous engineer and the inventor of the

steam hammer) and James Carpenter. First published in 1874, the authors

made serious efforts to understand the origins of the Moon and the evolu-

tion of its surface features (though their theories bear little relation to our

modern ideas). Much of their researches were based on observations made

with Nasmyth’s home-made 20-inch (0.51 m) reflector of novel design.

Incidentally, the optical arrangement Nasmyth originated is often used

in today’s largest telescopes and is known by his name. Nasmyth and

Carpenter’s book also contains beautiful drawings and photographs of

sculpted models of regions of the lunar surface (at that time, photography

had not technically advanced enough to enable good, detailed, photo-

graphs to be taken of the Moon’s surface direct through the telescope)

along with written descriptions.

Other notable books about the Moon included The Moon written by the

Englishman Edmund Nevill and published two years after Nasmyth and

Carpenter’s book of the same name. Actually, Nevill wrote under the name

Neison. His book contained a map based on that of Beer and Mädler, along

with detailed descriptions of the named features.


If, as a result of the necessary brevity of these historical notes,* I have

given the impression that selenography was only carried out by a few indi-

viduals then I must rectify that impression. For instance in England there

was the Selenographical Society, formed in the early 1870s specifically for

lunar studies. The British Association for the Advancement of Science appointed

the Secretary of the Society, W. R. Birt, to head a committee to organise the

construction of a new and more detailed map of the Moon. It was intended

to be 200 inches (5.08 m) to the diameter of the Moon. Birt was an energetic

selenographer and a start was made, though Birt’s death and the eventual

demise of the Selenographical Society in 1882 meant that the scheme did

not bear fruit.

Also, many national and provincial astronomical societies had sections

devoted to lunar study. One very active group of the period was the Liverpool

Astronomical Society. It’s director was T. G. Elger, who became the first direc-

tor of the Lunar Section of the British Astronomical Association when it

formed in 1890. In those early years many people spent a great many hours

at the eyepieces of their telescopes studying the Moon.

The last really substantial Moon map to be made using the old-fash-

ioned methods of eye and drawing board to record its finest details was the

300 inch (7.6 m to the Moon’s full diameter) colossus of H. P. Wilkins. He

published the first version of it in 1946 and made revisions in subsequent

years. At the time he was Director of the Lunar Section of the British

Astronomical Association. The only version of Wilkins’ map I have seen is

that reproduced in reduced scale in twenty-five sections in the book The

Moon by Wilkins and Patrick Moore, published by Faber and Faber in 1955.

I was lucky enough to find a copy of this work in a second-hand bookshop

some years ago, though it is now very rare. The complexity of the hand-

drawn details in the map is mind-boggling. Though it is now recognised

that Wilkins’ map contains many inaccuracies in its depictions of details

(I have stumbled across several, myself, without making any effort to find

them), the scale of his achievement still warrants admiration.

Photography, invented in the early nineteenth century, was sufficiently

developed to come to the aid of Moon-mappers in the last decade of the

nineteenth century and, particularly, those of the twentieth century – but

that is a tale for later in this book. Now, after this ‘potted’ history of the ear-

liest years of lunar study (admittedly leaving out much detail and not even

mentioning many of the more minor participants), it is time to consider

how the observer of today can get the best out of his/her telescope and

enjoy and study the Moon’s starkly beautiful vistas.

* Note added in proof: just published by Cambridge University Press is Mapping andNaming the Moon by E. A. Whitaker – a detailed and fascinating account of the historyof selenography.


Telescopes and drawing boards

Why bother to observe the Moon at all, let alone go to the trouble of

drawing it? Well, the answer to that is likely to be different for different

people. I tried to give you the essence of my personal obsession in the intro-

duction to Chapter 1. Given the fact that you are reading this book, I take

it that you have some interest in astronomy in general and, maybe, in the

Moon in particular. That at least justifies observing the Moon through a

telescope.

What about drawing the lunar surface, though? It is a lot more trouble

doing that than passively looking through the telescope eyepiece. Are the

results of your efforts going to be scientifically useful? A decade, or more,

ago and I would have said “Yes”, with a few provisos. Now, I have to admit

that there is very little new science to be gained through amateur drawings

of the lunar surface. If you wish to obtain high-quality topographic data on

the Moon then you would be best seeking out the Clementine and Lunar

Prospector space-probe data on the Internet, or on CD ROM. The various

lumps, bumps and other features are now mapped with much greater pre-

cision than can possibly be exceeded by an amateur’s eye, telescope and

pencil.

I have to be brutally honest. There is not really anything much the Moon

enthusiast can do at the telescope that is scientifically useful, other than

to time occultations (see Chapter 1) and to monitor the Moon’s surface for

transient phenomena and record any suspicious appearances in a variety

of media. This highly controversial field is discussed in Chapter 9.

There are a few minor queries and mysteries that the amateur might

help to solve (some of these are highlighted in Chapter 8) but, all in all, the

day of the amateur lunar cartographer is long past.

So, why draw the Moon? The mountain climber’s adage “because it is

there” might suffice as a reason. The Moon’s beautiful orb is every bit as

47

CHAPTER 3

much a part of nature as the mountains and valleys, fauna and flora here

on the Earth. Drawing the Moon’s surface details is also a powerful way of

communing with it. The process of doing so will also create a kinship

between you and the selenographers of yesteryear who had to draw the

Moon because there was no more sensitive way of doing it. You will cer-

tainly get to know the parts of the Moon you sketch with great intimacy.

You might never get to travel to the Moon but carefully observing it

through your telescope and drawing what you see through the eyepiece

surely comes as a good second-best.

Whatever your reasons for observing, and possibly drawing, the Moon,

I hope that you, like me, experience the strongest of all motives for doing

it – sheer enjoyment!

Of course, now we come to the ‘nitty gritty’ of actually doing it. First we

must consider the observer’s telescope. Unfortunately here I am up against

the economics of book production. Space is at a premium. So, can I at

this point refer you to my book Advanced Amateur Astronomy (Cambridge

University Press, second edition, 1997) where I provide general and wide-

ranging details about the different types of available telescopes and auxil-

iary equipment. You will also find there details of their setting up and the

necessary mechanical and optical adjustments. In the following sections I

offer just a few potted notes on matters of particular relevance to the lunar

observer.

First of all, please let me say that if you already own a telescope then

use that one for your lunar observing. You will be delighted with the details

of our neighbouring world that it can reveal. However, if you are planning

to build or buy some new equipment then there is scope (no pun intended!)

for making an informed choice. Failing that, there might be ways you can

improve your existing equipment to make it more useful for Moon observ-

ing. The following notes might help.

3.1 WHAT TYPE OF TELESCOPE DO YOU NEED?In many branches of observational astronomy a telescope’s light grasp is

crucial. In such cases a large aperture is normally an advantage. The Moon

is one of the few celestial objects that provides us with plenty of light. It

is the various other imaging characteristics of the telescope which are

most important for lunar and planetary observation. These can broadly be

grouped as resolving power and contrast, though there is a degree of inter-

relation between them.

The image a telescope makes of a point source (in practice, a star)

defines what we call the point-spread function, sometimes known as the

instrument profile, of it. The typical diffraction pattern of a star produced by

an unobstructed aperture is represented in Figure 3.1(a). Larger apertures

produce smaller diffraction patterns. It is the size of these diffraction pat-

48 TELESCOPES AND DRAWING BOARDS

3.1 WHAT TYPE OF TELESCOPE DO YOU NEED? 49

Figure 3.1(a) Idealisedrepresentation of thediffraction pattern of astar produced by anunobstructed aperture(for example a refractingtelescope). (b) In (i) a pairof stars are too closetogether for a given tele-scope to resolve thembecause the diffractionpatterns merge. In (ii) thestars are just resolvableand in (iii) they are easilyresolvable. The complexextended image that a tele-scope forms of the Mooncan be, albeit simplisti-cally, thought of as beingcomposed of an array ofstar-like points in order tounderstand the principleof resolution of it by agiven telescope.

(a)

(b)

terns that decides whether a telescope has the potential to resolve a close-

together pair of stars, or not. This is illustrated in Figure 3.1(b).

So much for stars. We are interested more in resolving details on an

extended body – the Moon. The same principle applies. The image the tele-

scope forms of the Moon can be thought of as being composed of a series

of overlapping diffraction patterns, each generated by a minute point in

the image. A handy way to grasp this is to think of the Moon’s image as a

mosaic. Obviously the size of the individual tiles determines the fineness

of detail that can be represented on the mosaic. If you use a larger telescope

the individual diffraction patterns are smaller. This is the same as having

the mosaic made up from smaller tiles.

The resolving power, R, of an unobstructed optical aperture is given by

R�137/D, (3.1)

where R is in arcseconds andD is the diameter of the aperture inmillimetres.

This formula is derived from Rayleigh’s mathematically derived limit and

the numerator (137) is true for the mean visual wavelength (540 nm). Many

readers will also be familiar with Dawes Limit. The formula takes the same

form but the numerator would be 116 in the above equation. In practice,

Rayleigh’s Limit gives a truer measure of resolution in images of extended

bodies. Note this limit is for detailswithmaximumcontrast – in otherwords,

blacks and whites. Low-contrast boundaries are less well delineated.

So, we need a larger telescope to see finer details on the Moon. Is that

the end of the matter? Actually, no. There is more to it than that. In practi-

cal telescopes the point-spread function is influenced by instrumental

design and the accuracy of manufacture of the optical surfaces. We also

have to contend with the prevailing atmospheric conditions, but more of

that complication later.

On the point about accuracy of manufacture of the optics, again I must

refer you to my Advanced Amateur Astronomy for a full discussion but I can

state here that all the rays collected by the telescope objective from one

point on the object ought to be brought to a coincident point in the final-

image plane to an accuracy of within 1⁄4-wavelength of yellow-green light.

If the ray fronts deviate by more than this amount, about 135 nm, then the

diffraction pattern will be noticeably spoilt. The point-spread function will

have been changed and both image resolution and contrast will suffer.

Even the 1⁄4-wavelength limit is not the ultimate. There would be some

improvement in a telescope’s performance if it had optics of greater accu-

racy. However, most of the performance can be realised at this universally

accepted benchmark of quality.

Of the most common telescope designs (and putting aside any subse-

quent modifications by the telescope-user), the instrument that comes


closest to providing the textbook diffraction pattern structure is the

refractor.

Refractors tend to have large focal ratios and this is often cited as a

reason why they give good images. Certainly, the relatively gentle curves

on optical surfaces with large focal ratios are easier to manufacture with

accuracy and this is one reason why refractors make good telescopes for

Moon and planet observing. Actually, it is quite possible also to make reflec-

tors with long focal lengths, so this is not an exclusive property of refrac-

tors. In addition, large focal ratios allow the simpler designs of eyepieces to

function better and this is one real reason for large focal ratios being per-

ceived as delivering better images.

Moreover, refractors generally have to have large focal ratios because of

a generic problem with them. While the manufacturer designs the refrac-

tor to bring the wavelength to which the eye is most sensitive (540 nm) to

a minimum focus, inevitably the correct focal positions for the other wave-

lengths occupy a range of positions extending further from the lens than

the minimum focus. This secondary spectrum generally shows itself as a sof-

tening of contours in the image, together with a reduction in image con-

trast, and even visible colour-fringing when the problem is severe. Of

course, what is tolerable depends upon what one is doing. In any case,

the effect of the secondary spectrum diminishes with the square of the

focal ratio for the range of sizes and focal ratios normally encountered.

Incidentally, the wavefront error (change of focus) for the extreme ends of

the spectrum (red and violet light) compared to the yellow-green light can

be several times the limit tolerable for the seidal errors (spherical aberra-

tion, coma, astigmatism, field curvature and distortion) because of the

reduced sensitivity of the eye at wavelengths away from that of yellow-

green light.

I have used a number of refractors, both large and small over the years.

Based upon my experiences with them I would say that for general lunar

work ‘old fashioned’ two-element achromatic object glasses ought to have

a focal ratio of, at the very least, 1.3 times the aperture in inches (0.06

times the aperture in millimetres) in order that the secondary spectrum

is not too prominent. Even then the image will not be perfect. As a case

in point, I often used the 12.8-inch (325 mm) f/16.4 ‘Mertz’ refractor which

was mounted on the ‘Thompson’ 26-inch (0.66 m) astrographic refractor

at Herstmonceux. With it, the Moon’s craters were fringed with yellow

and the black shadows were filled in with a delicate blue haze! By con-

trast, the 7-inch (178 mm) f/24 refractor that was mounted on the 36-inch

(0.91 m) Cassegrain reflector (the ‘Yapp reflector’) on the same site gave

images of the Moon that were very haze-free and totally free of false

colour-fringing.


A few companies, notably Meade, market modern refractors with one

component of the two-element objectives made of a special glass. The

result is a refractor with a much reduced secondary spectrum compared to

one of classical design. These are marketed as ‘apochromatic’, though that

title really belongs to three-element objectives. These have the smallest sec-

ondary spectrum (about one-ninth of that of the classical objective of the

same focal ratio). The modern two-element ‘apochromatic’ refractors (they

should really be called semi-apochromatic) are much better than the clas-

sical ones but not as good as the true triplet apochromatic instruments in

terms of the secondary spectra they produce. They are mainly produced

with focal ratios of about f/9 and in sizes up to 7-inch (178 mm) aperture.

They are expensive for their size but do give superb images.

In the past few years, the Schmidt–Cassegrain (and its close cousin, the

Maksutov–Cassegrain) telescopes have become extremely popular. Indeed,

they may well be becoming the most popular of purchased telescopes.

Their compactness, and even portability, lend themselves to the needs of

the modern amateur astronomer very well. They are expensive but, for the

price, you typically get a computer-controlled instrument that can auto-

matically set and track on any of thousands of celestial objects.

All very well, but how good are they for observing the Moon? Well, if

you need computer control to set your telescope to the Moon then some-

thing is very wrong! Of course, the portability and compactness aspects are

just as much of an advantage to the Moon observer. The downside is that,

aperture-for-aperture, they do not give quite as good lunar and planetary

images as many other types of telescope.

The reasons are two-fold. One is that the steep curve on the primary

mirror (typically about f/2.5 – this is what makes the instruments compact)

and the complex curve on the corrector plate (for the Schmidt–Cassegrain,

which is the most common type in production; the Maksutov–Cassegrain

has a meniscus corrector) are both difficult to manufacture accurately by

production-line methods. Inevitably, the optical surfaces will fall just a

little short of the ideal accuracy and so the wavefront error will probably

be larger than the desired minimum of 1⁄4-wavelength of yellow-green light.

The second reason is common to all telescopes with a central obstruc-

tion in the light-path. The central obstruction modifies the diffraction

pattern structure. Light is taken from the central disk and given to the

rings. This modification of the point-spread function only slightly impairs

resolution within an image composed of a pattern of blacks and whites.

However, it seriously reduces the visibility and resolution of low-contrast

details, especially where those low-contrast markings appear against a

bright background. This is usually the case for seeing details on the

planets. While it is true that details seen along the Moon’s terminator are


mostly nearly-blacks and nearly-whites, there are subtle shadings which

also form part of the scene. In addition, the reduction of contrast is worst

for the smallest details in the image, making things very hard to discern

near the diffraction limit. The central obstructions of Schmidt–Cassegrain

telescopes are usually at least one-third of the total diameter, the largest

for any type of telescope commonly in amateur hands.

The two problems, shortfall in optical accuracy and the central obstruc-

tion, each produce additive effects on the point-spread function. The

common f/10 Schmidt–Cassegrain telescopes on sale have to have apertures

around twice as large as the best refractors in order to show the Moon and

planets as well under identical excellent conditions.

The telescope that still gives the observer the best value for money is the

Newtonian reflector. Any manufacturer can produce a poor Newtonian

telescope but at least it is not too difficult for the manufacturer to produce

a good one. The obstruction due to the secondary mirror tends to be about

one-quarter of the telescope aperture and providing the mirrors are of

high optical quality the resulting Newtonian telescope will produce better

Moon and planet images than will the Schmidt–Cassegrain of the same

aperture, though still down on what the good refractor can show. However,

it will be much cheaper than both.

If you decide to buy or build a Newtonian reflector specifically for

observing the Moon and the planets, go for a focal length as large as is prac-

tical for your situation (size of garden, size of observatory, etc.), while

ensuring that it is firmly mounted. A gangling, spindly affair will flutter in

the breeze and shudder with every touch of the focuser – not something

that is conducive to good observing!

For purely visual work the telescope need not be driven. Of course, a

drive is an advantage as long as it works properly. The requirements for

photography and electronic imaging are discussed in later chapters in this

book.

Should the telescope have an open framework tube, or one that is solid?

The ultimate in baffling against stray light is not essential for Moon and

planet work but warm air from the observer can cause problems if it gets

into the telescope’s light-path. A solid tube prevents this to some extent.

However, convective tube currents generated by warm optics and fittings

can also degrade the image produced by solid-tubed reflectors. In particu-

lar, the thermal lag of the primary mirror can give a lot of trouble. Here,

an open tube is an advantage. Vents, and even electric fans installed near

the telescope primary mirror, can help matters. My 181⁄4-inch (0.46 m) reflec-

tor has an open-framework tube, while my 81⁄2-inch (216 mm) has a solid

tube. On some nights the images produced by the 81⁄2-inch are poor and star

images betray the obvious presence of a tube current (sorry, again I must


refer you to my Advanced Amateur Astronomy for explanations and details).

There is a door installed in the tube close to the primary mirror (see Figure

3.2) to gain access to the mirror cover. Opening this door significantly

improves the images on those nights, since it lets much of the warm air

convected from the primary mirror to escape, rather than passing up the

entire length of the tube.

In conclusion, I think the best design is to have the telescope tube partly

closed, especially near the eyepiece. It should, though, be open near the

primary mirror (or at least well ventilated) to suppress tube currents.

Having the mirrors cool quickly is also desirable to suppress tube cur-

rents. A thicker-than-necessary primary mirror and an unventilated cell

will work against this. Closed optical systems, such as refractors and

Schmidt–Cassegrain telescopes, are less troubled by tube currents, though

both need to cool off for a while if brought out from indoors before

observing.

Cassegrain telescopes are expensive and tricky to collimate. They are

rare among modern amateur astronomers. The secondary obstruction is

usually a little larger than that of the Newtonian but they do share the

advantage of the Schmidt–Cassegrain in having a long effective focal

length in a short tube assembly.

For general (mainly visual) observing of the Moon and planets I would

recommend the modern semi-apochromatic refractor if money is of no

object. If value for money is sought, I would say go for the Newtonian reflec-

tor. It is also the telescope most adaptable for other types of work. Of the


Figure 3.2 The door in theauthor’s solid-tubed 81⁄2-inch (216 mm) Newtonianreflector giving access tothe primary mirror cover.It is also useful in ventilat-ing the mirror and cell, sominimising tube currents.

other common types, the production Schmidt–Cassegrains would be my

third choice because classical Cassegrains would likely cost more, size-for-

size, even though they should give better images.

So much for type. What about size?

3.2 HOW BIG A TELESCOPE DO YOU NEED?If the optical transmission characteristics of the Earth’s atmosphere were

perfect and the telescope was in a perfectly temperature-stable environ-

ment, then it would be a case of ‘the bigger the better’ as far as the aper-

ture of the telescope goes. The one caveat is that size must never be at the

expense of quality.

Of course, the telescope is not in a temperature-stable environment and

the normal observing conditions are anything but perfect – and that

changes matters very considerably.

I still put quality above sheer size when it comes to selecting telescopic

equipment. You will have a great deal more satisfaction from working with

a telescope of good mechanical and optical quality of moderate, or even

small, size than you will from a much larger light-bucket. If your budget

can stretch to a first-class 6-inch (152 mm) telescope or a mediocre 8-inch

(203 mm) one, or even a tempting but poor-quality 10-inch (254 mm) instru-

ment, put out of your mind any thoughts about impressing your neigh-

bours and friends and go for the 6-inch instead. I guarantee that if you

could try all three together one night for Moon observing, it would be the

smallest one that would give you the best view and the greatest pleasure as

a result.

What if one is rich enough to have quality and size? Will a bigger tele-

scope always outperform a smaller one of equal quality? Based on my thirty

years of experience of lunar observing with a large variety of telescopes of

differing size and design (ranging from a 60 mm refractor to a 0.91 m

Cassegrain reflector), my answer to that question is “No”. In fact, some-

times even the reverse is true. Understanding why this should be so is not

very difficult. There are two main reasons.

Firstly, the column of air through which the telescope is looking is

seething with convective pockets, or cells, of air of slightly differing temper-

atures, and hence differing density and refractive index. The ones that affect

the telescopist to the greatest extend are from 10 to 20 cm in diameter and

can occur from just in front of the telescope to many kilometres in height.

Each of these cells disturbs the passage of light-rays passing though it. The

result is that the telescope cannot produce a sharp and steady image at its

focus. The blurred and mobile (we say turbulent or bad seeing) image that

results is well known to all telescope users. However, most do not appre-

ciate just how severe the limitation really is. From most backyard sites the

3.2 HOW BIG A TELESCOPE DO YOU NEED? 55

seeing rarely allows details to be resolved that are finer than about 1 arc-

second in extent. For an object situated at the Moon’s distance this is a

linear dimension of about 1 mile (about 1.6 km).

A good-quality 6-inch telescope will allow you to resolve this level of

detail. A bigger instrument will not show you any finer detail on those

‘1 arcsecond’ nights. Of course the image will be brighter when seen

through the bigger telescope and the contrast of the image (at least for

coarse details) will be greater, the comparison being made at a given, ade-

quate, magnification. In ordinary conditions, the advantage of large aper-

tures in seeing faint planetary markings (and delicate shadings on the

Moon) is not as great as one might expect. While I have experienced rare

nights where my 181⁄4-inch (0.46 m) telescope shows views of Jupiter and

Saturn reminiscent of Voyager space-probe images, I must say that the

normal view is much fuzzier and washed-out. On those normal nights I

find that my 81⁄2-inch telescope can show these bodies just as well as my

181⁄4-inch.

Indeed, sometimes the bigger telescope will produce significantly

poorer images than will the smaller one. If the small-aperture telescope

can look through just one convective cell of air at a time, then the image

will ‘slurp’ around its mean position and may distort. However, it will

remain quite sharply defined. If the telescope aperture is bigger, then it is

looking through a column of air that may include several convective air

cells at any one moment. Each cell will produce its own, random, effect and

the telescope will combine them. This time, the image will be composed of

a number of overlapping components, each one shifting and distorting in

a separate way. The end result is a confused and blurred image. It may often

be preferable to have the one sharply defined, but admittedly gyrating and

distorting, image rather than the confused mess.

The second reason why a bigger telescope is not always better was dis-

cussed in the last section – namely thermal effects. The smaller the mass

of the telescope, the quicker will it cool to the ambient temperature and so

not be troubled by convective currents of air from its optics and fittings.

Optical surfaces can also badly distort in steep temperature gradients.

All in all, if you can afford it, I would say go for a Newtonian reflector

of 10-inch – 16-inch (254 mm – 406 mm) aperture and as large a focal ratio

as you can reasonably accommodate. Bear in mind, though, that the

number of nights that you will get full performance, even from a 10-inch,

will be very few if your site is anything like mine! If your observing site is

consistently poor, as regards atmospheric turbulence, then you may be

better off with a 6-inch (152 mm) or 7-inch (178 mm) ‘apochromatic’ f/9, or

f/14–f/20 achromatic, refractor at a similar cost (several thousands of

pounds/dollars, plus the cost of housing it).


3.3 EYEPIECES AND MAGNIFICATION

Full descriptions of the types of eyepieces and their imaging characteris-

tics are given in, you guessed it, Advanced Amateur Astronomy. In general, if

the effective focal ratio of the telescope is f/10 or more, then any of the

simpler types will be suitable for lunar observing. Ramsden, Achromatic

Ramsden and Kellner eyepieces are commonly available and the modern

ones invariably have bloomed (anti-reflection coated) lenses. Blooming is

highly desirable in order to avoid annoying inter-glass reflections and a

general reduction of image contrast. They differ in field size. Ramsdens

have apparent fields of about 35°, while the other two generally have appar-

ent fields of about 40° and will give good images in f/6 telescopes with focal

lengths longer than 12 mm. (Actual field�Apparent field/Magnification, so

a Kellner eyepiece might give a field of 1⁄4° if it produces a magnification of

�160 with a given telescope). Ramsdens will not work well with telescopes

of ratios lower than f/10. A general softening of the image and even colour-

fringing will be visible when used on lower focal ratios.

Classical Huygenian eyepieces should not be used with focal ratios of

less than about f/10 but the modern continental ones generally have a

modified design and can work well with focal ratios down to about f/8. They

have apparent fields of view around 30°.

The best type of eyepiece for lunar and planetary observation, the

Monocentric, seems to be incredibly rare these days. This cemented triplet

gives crisp and false-colour-free images even with f/5 telescopes, the disad-

vantage being a smallish field of view (apparent field about 30°). I wish they

were still available. The Tolles eyepiece is really a solid (one piece of glass)

version of the Huygenian eyepiece. The field of view is small (25–30°). Now

obsolete, it also used to be a favourite of planetary observers, producing

crisp and false-colour-free images with focal ratios down to about f/7.

If you have a telescope of focal ratio f/10 or less and want modern eye-

pieces for lunar and planetary observation then you will be best served by

the easily available Plössyl type. They typically have fields of view of around

50–55° and produce high-quality images with any telescope of focal ratio

above f/5. They have largely superseded Orthoscopics as the choice four-

element eyepiece, even though the finest examples of the Orthoscopics are

slightly superior in imaging characteristics (except size of the field of view

– apparent field diameter 40–45°) to the Plössyl type.

Apart from the possible exception of Nagler eyepieces (which can also

work well with focal ratios down to f/4.5, maybe even f/4), I would not rec-

ommend using any of the wide-field eyepieces for lunar and planetary

observation, as most lack critical definition and some are troubled by scat-

tered light and ghost images, despite blooming.

Barlow lenses can be useful. The most common form of this accessory

3.3 EYEPIECES AND MAGNIFICATION 57

consists of a diverging (convex or plano–convex) doublet lens set into one

end of a tube, or series of tubes. This end is plugged into the telescope draw-

tube while the eyepiece is plugged into the other. The reduction of the con-

vergence of the rays from the telescope objective has the consequence of

multiplying the effective focal length of the telescope by a given factor. This

is usually �2 but can be anything the manufacturer desires. All this will

be common knowledge to most readers. However, not all may realise that

the effective focal ratio (EFR) of the telescope is multiplied by the same

factor. Thus an f/5 telescope is converted to an f/10 one, using a �2 Barlow.

As well as the obvious multiplication of the magnification of the telescope

by a given eyepiece, using the Barlow lens allows the simpler (and cheaper!)

eyepieces to be used if so desired.

One note of caution, though; adding more lens elements into the

optical path will increase the amount of light absorbed and scattered. Of

course, blooming, and ensuring the lenses are scrupulously clean (not

always easy to do) will go a long way to negating this. Also the Barlow lens

must be of high optical quality if it is not to degrade the view produced by

the telescope. Regrettably, this is not always the case.

In particular, if your telescope has a focal ratio of less than f/6 I would

caution that a common two-element Barlow lens will introduce enough

chromatic aberration to produce noticeable colour-fringing when used

with powerful (focal length less than a centimetre) eyepieces. Some manu-

facturers supply triplet (apochromatic) Barlow lenses and I would recom-

mend you obtain one of these if you want to use it with a reflecting

telescope of low focal ratio. By easing the load on your eyepieces, a first-rate

apochromatic Barlow lens may actually upgrade the quality of the images

your low focal ratio telescope can produce, despite any slight negation due

to scattered light. In addition, a few well-chosen eyepieces are sufficient, if

used in conjunction with one or more Barlow lenses, to deliver a large

range of magnifications with a given telescope.

What about the actual values of magnification? Here I must stress that

personal preference must rule the day. Having one eyepiece in which you

can view the entire Moon in one go is highly desirable, especially for occa-

sions such as eclipses. The actual field imaged must therefore not be less

than about 0°.6. This means a magnification of no more than about �66

(for an eyepiece with a 40° apparent field) to �86 (52° apparent field eye-

piece). Having a set of eyepieces that can deliver a series of higher magnifi-

cations (and perhaps a Barlow lens to help fill in the steps) is also desirable.

If the observing conditions were perfect (and the telescope were of good

quality) then I would normally prefer a magnification roughly equal to the

aperture of the telescope measured in millimetres. However, ‘fussy’ detail,

such as the individual peaks in a lunar mountain range, might be better


appreciated with higher powers, perhaps up to �2 per millimetre of aper-

ture. Poorer conditions demand lower powers, of course, as do broad fea-

tures of low contrast.

Most of my lunar observing is done with powers of �144 and �207 with

my 181⁄4-inch (0.46 m) reflector because of the usual, 1 arcsecond, seeing

conditions at my observing site. Even then, the 1 arcsecond figure refers to

the brief glimpses of fine detail, not the average amount of blurring and

distortion which amounts to several times this value. I seldom see any real

advantage to using higher powers, though on a few outstanding nights I

have had incredible views at �432. Sadly, those instances have been very

few and far between – how I wish it were otherwise!.

3.4 MAKING THE BEST OF WHAT YOU HAVE

Let us say that you have a great big ‘light-bucket’ of a Newtonian reflector

with a low focal ratio, mediocre optics, and a large secondary mirror.

Perhaps it is one of the cheaply produced large Dobsonian-mounted tele-

scopes. It will come supplied with one or more low-cost eyepieces. You find

it gives very bright but disappointingly blurred images of the Moon. Can

you improve matters without having to buy another telescope? I am glad

to say that the answer is “Yes”.

Let us consider the eyepieces. The set that the light-bucket has will

undoubtedly work better with a telescope of higher effective focal ratio

(EFR). If your telescope has a focal ratio lower than f/5 or f/6, then you might

be advised to obtain a triplet (truly apochromatic) Barlow lens in order to

raise its effective focal ratio, as described in the foregoing section. A more

expensive alternative is, of course, to buy a higher-quality set of eyepieces.

The foregoing notes should help you make the choice.

What about that big secondary mirror? You might like to consider

replacing it with a smaller one. However, you can’t make it too small or you

will effectively stop-down your telescope (unless that is a deliberate choice

– large cheap primary mirrors are often of poorest accuracy in their outer

zones, so blanking off these zones may actually improve the image

quality!). If the distance from the telescope focal plane to the secondary

mirror, measured along the optical axis, is A and the focal ratio of the tele-

scope is f, then the minimum diameter d of the minor axis of the secon-

dary mirror, A, has to be:

d�A/f, (3.2)

where d, A and f are all measured in the same units. This bare-minimum

diameter just allows the very centre of the field of view to be fully illumi-

nated by the rays from the entire primary mirror surface. There will be

some vignetting of the rays away from the centre of the field of view.

3.4 MAKING THE BEST OF WHAT YOU HAVE 59

However, you will find that for purely visual work you will not notice the

slight dimming of the image towards the edge of the field of view. Of

course, if the telescope had a larger focal ratio to start with, it could already

have a secondary mirror that is very small. Despite the outfield vignetting,

the image contrast will be at a maximum when the size of the secondary

obstruction is at a minimum, as outlined earlier.

The advantages of using off-axis stops over the telescope aperture is

hotly disputed. My own experience is that stopping my 181⁄4-inch (0.46 m)

telescope down to 6 inches (152 mm) with a cardboard diaphragm some-

times improves the images the telescope delivers. When the seeing is par-

ticularly rough and the images of details tend to be multiple and confused

the stop sometimes ‘cleans up’ the view, as described earlier.

Certainly if the optics of the telescope are of poor quality, then stopping

the instrument down will usually imporve matters, whatever the seeing.

Also the diffraction pattern produced, using the stop, is more refractor-

like, even if it is broader because the aperture generating it is smaller.

Obviously, the hole in the diaphragm is made and positioned to avoid the

secondary mirror and its support vanes (see Figure 3.3). A 16-inch to 20-inch

‘light-bucket’ may be made to perform like a high-quality 5-inch to 7-inch

refractor in this way. Try this for yourself. All it takes is a few minutes to


Figure 3.3 An off-axis stopfor a reflecting telescope.Unless the mirror is thinenough to distort along itslower edge (unlikely inamateur-sized telescopes)positioning the apertureto expose the lower part ofthe mirror will normallyprovide the best images.This is because all of themirror surface will nor-mally produce upwardlymoving convective warmair currents. Positioningthe aperture over thelower regions minimisesthe amount of convectingair the light rays have topass through.

mark and cut out a piece of cardboard to suit your telescope. However, I

would caution you to only use the diaphragm if you see a definite improve-

ment in the image. Otherwise the diffraction limit imposed by the reduced

aperture might mean that you miss the occasional flashes of fine detail

that one usually gets on even poor nights.

If your telescope is deficient in its mechanical construction then

perhaps you can make or purchase some replacement parts to improve

matters. If the optics are good you might even think about rebuilding the

instrument and just salvaging some of the parts of the original. At the

same time you can make any changes that will improve its thermal charac-

teristics. However, that is taking us into matters which are beyond the

remit for this book. Let us now, at long last, get down to some actual observ-

ing and drawing of the Moon’s beautiful vistas . . . .

3.5 DRAWING THE MOON

Given the telescope, the basic equipment consists of some sort of clipboard

with a source of attached illumination. A small piece of hardboard, or a

large dinner mat, a switch, a torch bulb and holder, a small square card-

board or metal box (to mount the bulb in its holder at the head of the

board), a switch, some wire, a battery (perhaps mounted on the board by

means of a Terry-clip) and terminal connections (or soldered joints), or

alternative materials, can easily be fashioned into something appropriate.

Adding direct shielding from the bulb is also desirable and a small rheo-

stat is also useful for brightness control. However, keep it simple and, above

all, keep it lightweight.

Your drawing can be a simple line-diagram. At the other extreme it can

be a photographic quality work of art showing all the half-tones. What is

possible depends on your abilities. This will, of course, improve with prac-

tice. Even if your work is not to be used for cutting-edge research, astron-

omy is still a science. Therefore your drawing must be accurate. Your

fellow astronomers will think little of the most picturesque representation

that you can produce if it is inaccurate in its proportions and positions.

Even the simplest representation that is accurate is always vastly

preferable.

I ought to emphasise that there are many ways of achieving good rep-

resentations of the Moon’s surface. There is a large array of materials –

pencil, pen, ink, charcoal, paint, etc. – to be used on an equally large array

of papers, canvases, etc. Each will demand its own techniques. Moreover,

each individual will undoubtedly find various ways of working that suit

him/her best. Consequently, all I will do here is to offer a few guidelines,

based on my experience, which is very limited when it comes to drawing

the Moon, and that of others who are more experienced.

3.5 DRAWING THE MOON 61

Andrew Johnson is one of a number of amateur astronomers produc-

ing superb representations of the lunar surface. He has written an article

outlining his own methods, and giving good general advice for the tyro,

in the Association of Lunar and Planetary Observers (ALPO) publication The

Strolling Astronomer (Volume 37, Number 1, May 1993, pages 18–23). Andrew has

generously let me reproduce some of the illustrations from that article

here. The good advice he gives is pretty universal and much is the same as

that given herewith. Even so, if you are seriously interested in making

high-quality drawings of the Moon then I recommend you seek out his

article. I am most definitely not one of the ‘grand masters’ of lunar

drawing. He is.

When you first go to your telescope try not to spend too much time

deciding what to draw. At least having an outline plan for the evening will

save you a lot of time and effort when you should be actively observing,

even though unpredictable weather and observing conditions will demand

some flexibility on your part.

Having decided on your chosen target, spend a while scrutinising it

with different magnifications before committing anything to paper. Do

not attempt to take in a large area in one go. The area you should cover in

your drawing should certainly not be greater than about 200 km square on

the lunar surface. Better still if it is smaller. When you are about ready to

begin drawing, aim for a scale of at least 2 km per millimetre.

Considering just the simplest line drawings, you might generate the

sketch entirely from the view through the telescope straight on to a blank

sheet of paper. If so, you will achieve the best accuracy by starting with a

set of faint pencil guidelines to help you with the proportions. This is illus-

trated in Figure 3.4(a), which shows the first stage of a drawing of the crater

Mairan by Andrew Johnson. Keeping the guidelines very light allows them

to be erased easily once the major details are blocked in, as they have been

in Figure 3.4(b).

Alternatively, you could base your sketch on a pre-prepared outline of

the major features. Your work at the telescope would then consist of filling

in the fine details and the shadows. You might make an outline by tracing

over a suitable photograph. This technique ought to produce a greater posi-

tional accuracy in the drawing, though you must not ignore the effects of

libration, especially for features near the lunar limb. The libration value at

the time of your drawing is unlikely to be similar to that when the photo-

graph was taken.

The real Moon has shades of grey on it, as well as blacks and whites.

There are a number of ways you can represent these on your drawing. One

is to add numbers to the areas, representing brightness gradations. Figure

3.4(c) shows the next stage in Andrew Johnson’s drawing of Mairan. On the


scale Andrew has used 0 represents black and 10 represents brilliant white.

This can be the finished product.

Alternatively, the outline sketch can be carefully traced and, using the

numbered original, the shades of grey can be built on in pencil, or what

other medium is chosen on the copy. Most of the really first-rate lunar

artists use this approach. Obviously, the finished version of the drawing is

made after the observing session. This demands that everything is meticu-

lously noted during the observation. Never rely on your memory of what

you think you saw through the eyepiece of the telescope. Get it right at the

telescope and you will have no temptation to make subsequent alterations

to your drawing.

When you have finished your initial sketch, spend a little time compar-

ing it with the scene through the eyepiece. Any perceived inadequacies of

your drawing that you do not feel able to correct can always be noted along

with it, e.g. ‘small crater should be drawn 20 per cent larger’, etc. Do not

forget to include all the usual details of date, time, instrumental details,

magnifications, seeing conditions.

You might prefer to make your final version at the telescope, complete

with all shades of grey and the black shadows filled in. I have found that

this is only possible if you work with very small, and hence simple, areas of

the lunar surface. Close to the terminator the shadows change noticeably

in just a few minutes. While it is certainly true that you can lay the outline

down and then note the time, subsequently spending time doing the shad-

ings, you will find that there is simply not enough time to do a complicated

drawing before the lighting over the scene changes too much. Ideally you

ought to complete your sketch within half-an-hour.

If you do want to do the whole thing, and produce the finished drawing

at the telescope, it is highly desirable you take steps to save time and so work

with maximum efficiency during the observation period. Having a pre-pre-

pared outline is particularly useful, as is greying the picture area of your

paper before hand. You could use pencil shading for this, or even sprinkling

on a little charcoal powder, in either case then smoothing with the finger.

At the telescope, a clean rubber can be used for creating the lighter areas

and a sharply pointed rubber effectively doubles as a ‘white pencil’. Darker

shadings can be built up with pencil, and black felt-tip pens, with fine and

broad tips as appropriate, can be used to create the black shadows.

If you decide to produce the final version of your drawing after the

observing session then, as already stated, the ways you can do it are almost

unlimited. However, not all methods will be conducive to subsequent

copying. Having back-up copies and copies to send to observing groups,

etc., is often desirable. The cheapest, simplest, and most widely available

method of copying, these days, is by way of a Xerox or other photocopying


machine. These can reproduce any image composed of lines and dots very

accurately. Unfortunately, photocopy machines often do not reproduce

half-tone images very well. Consequently, many lunar artists use stippling

as a way of representing half-tone shadings in their finished drawings. In

his The Strolling Astronomer article, Andrew Johnson suggests using a pen

(the choice ranging from the expensive professional drafting pens, to the

cheap but less durable felt-tips) with a point diameter of 0.3 mm. With

great patience the shadings are built up, dot by dot. Andrew uses a desk-

mounted magnifying glass, and provides good illumination to ease eye

strain. The greater the density of the dots, the darker the shading when


(a) (b)

(c) (d)

the drawing is viewed from the normal distance. Andrew typically takes

around 2 hours to produce the finished version of one of his drawings.

Figure 3.4(d) shows the process underway for his Mairan observation and

Figure 3.4(e) shows the final result.

Personally, the whole stippling process makes me exhausted just think-

ing about it! Nonetheless Andrew’s output is very high, as is that of his co-

workers, including Nigel Longshaw and Roy Bridge. Many examples of their

fine work are shown in the ‘A to Z’ section of this book, Chapter 8. You will

find there many examples of how they represent different types of forma-

tions and lighting aspects.


Figure 3.4(a)–(e) Stages inthe drawing of the lunarcrater Mairan by AndrewJohnson. See text fordetails.

(e)

In addition, all three acknowledge the legendary Harold Hill as the

supreme master of lunar drawing and the stippling process. He has been

studying and drawing the Moon’s vistas for over five decades and many of

his superlative drawings are shown in his A Portfolio of Lunar Drawings, pub-

lished by Cambridge University Press, 1991.


Figure 3.5 One alternativeto the stippling techniqueis cross-hatching, hereillustrated in a drawing ofMontes Alpes and MonsPiton by Andrew Johnson.

If the sheer labour of the stippling process puts you off, you might try

normal pencil shadings but on stippled paper (obtainable from an art

shop), or with normal paper placed over coarse sandpaper. This will create

‘pseudo-stippling’ which will photocopy much better than plain shading

alone. Varying the pressure of the pencil creates larger or smaller dots, pro-

ducing the required shading variations when viewed from the normal dis-

tance. Nonetheless, the best result will come from true stippling.

An alternative to stippling that will still photocopy well is cross-hatch-

ing. Figure 3.5 shows a striking example of this method produced by

Andrew Johnson. Of course, if appropriate copying methods (laser copier,

computer-scanner with ‘photo-quality’ output, etc.) are used, then less-

arduous methods can be used to make the final drawing.

One rung up the technological ladder from making drawings of the

Moon is to photograph it. That is the subject of the next chapter.


The Moon in camera

The first years of the nineteenth century saw the invention and develop-

ment of photography. The early processes and photographic materials were

clumsy and insensitive but a few determined individuals tried their best to

record images of astronomical bodies. J. W. Draper, of New York, is usually

credited as the first to achieve significant success in photographing the

Moon. In the Scientific Memoirs of 1840 he writes:

There is no difficulty in procuring impressions of the Moon by theDaguerreotype. By the aid of a lens and a heliostat, I caused the moonbeamsto converge on the plate, the lens being three inches in diameter. In half anhour a very strong impression was obtained. With another arrangement oflenses I obtained a stain nearly an inch in diameter, and of the general figureof the Moon, in which the places of the dark spots might be indistinctlytraced.

A decade later J. A. Whipple, also in the USA, succeeded in producing a

series of Daguerreotypes of the Moon at various lunar phases. The English

amateur Warren de la Rue achieved better results shortly after, as did Lewis

Rutherfurd in America. By the close of the nineteenth century the quality

of the photographs obtained had improved to the point that the first photo-

graphic atlases of the Moon could be compiled.

For example, W. H. Pickering published a complete photographic atlas

of the Moon in 1904. The plates were taken at the focus of a specially con-

structed 12-inch (305 mm) objective. Each region of the Moon was photo-

graphed under five different lighting angles, though the scale was not

large enough to show the smallest details on the lunar surface. The best

lunar photographic atlas of the period was that produced by M. Loewy and

P. Puiseux of the Paris Observatory. They employed the 23.6-inch (0.6 m)

coudé refractor there between 1896 and 1909 to take the plates for their

Atlas de la Lune.

69

CHAPTER 4

As the years rolled on the prospect of space probes, and even manned

missions, to the Moon spurred on further efforts. G. P. Kuiper and his col-

leagues published the Photographic Lunar Atlas in 1960. This was a boxed set

of large photographs of the Moon, the best examples of images from Mount

Wilson, Lick, Pic du Midi, MacDonald and Yerkes Observatories.

Under the auspices of the United States Air Force (USAF), Zdenek

Kopal headed the ‘Manchester Group’ (based at England’s Manchester

University), carrying out photography from Pic du Midi Observatory from

1959 to the 1970s. Situated high in the French Pyrenees the seeing at

the Pic was (and is!) superb. Initially the chief instrument used was a

23.6-inch refractor, the object glass of which was the very same as that

previously installed in the instrument used by Loewy and Puiseux at the

Paris Observatory. One member of the Manchester Group, Dr Thomas W.

Rackham, had special responsibility for the work with this refractor,

though other group members also took part.

Well over sixty thousand photographs were eventually obtained, from

which the Lunar Air Force Charts were constructed. The photographs were

good enough to enable relative heights on the lunar surface to be deter-

mined (by means of measurements of the cast shadows) with an accuracy

of a few metres in many cases.

The sub-arcsecond seeing typical at the Pic prompted the ‘Manchester

Group’ to procure for the observatory a 43-inch (1.07 m) Cassegrain reflec-

tor of design and optical quality especially suited to lunar and planetary

imaging. The various members of the ‘Manchester Group’, Patrick Sudbury

having special responsibility for the use of this instrument, began photo-

graphic work with it in 1964. Meanwhile they also collaborated with

Professor S. Miyamoto and his colleagues in Japan, (again under the aus-

pices of the USAF and NASA) in further photographic lunar cartography,

adding the 74-inch (1.9 m) reflector at Kottamia in Egypt to their arsenal.

Dr Rackham has very kindly let me reproduce a number of the photographs

taken at Kottamia in this book.

The enormously productive ‘Manchester Group’ were not the only major

players in the lunar mapping game. Gerard P. Kuiper, Ewen A. Whitaker,

along with Messrs Strom, Fountain and Larson of the Lunar and Planetary

Laboratory, based at the University of Arizona, in America, were also active.

They produced their superb Consolidated Lunar Atlas, consisting of the best 227

photographs of the Moon taken with the 61-inch (1.54 m) Naval Observatory

astrometric reflector and the 61-inch reflector on Catalina Mountain, in

Arizona. Most of the work (over 8000 negatives actually exposed) was done

with the Catalina telescope between 1965 and 1967. You will find sectional

enlargements made from many of the Catalina photographs in this book,

thanks to the kindness of Professor Whitaker and the University of Arizona.

70 THE MOON IN CAMERA

The professional programmes of Moon-mapping were essential to the

up-and-coming space missions. Amateur astronomers also tried their hand

at photographing the Moon. Many were very successful, even if the typical

backyard observing conditions rarely allowed sub-arcsecond resolution to

be achieved in their photographs.

During the 1960s one individual even emulated the professionals and

produced a photographic atlas that was commercially published. I refer to

the very useful Amateur Astronomer’s Photographic Lunar Atlas by Commander

H. R. Hatfield. In it the Moon is divided into 25 sections, for each there

being a detailed key map and several photographs taken under different

lighting conditions. Commander Hatfield even built the 12-inch (305 mm)

Newtonian reflector and the observatory that housed it himself, as well as

much of his photographic equipment. Although the first edition is now

long out of print (it was published by Lutterworth Press in 1968) second-

hand copies of it are still to be found. I often refer to mine. There is good

news in that Commander Hatfield’s Atlas is to be revised and re-published

by Springer–Verlag. At the time I write these words it is still in production

but should be available by the time this book is. It is now called The Hatfield

Photographic Lunar Atlas and the new edition has been edited by Jeremy Cook.

Georges Viscardy must rank as the premier amateur lunar photogra-

pher of recent years because of his very high output of lunar photographs

rivalling the professional efforts in their quality and resolution. He has a

201⁄2-inch (0.52 m) Cassegrain reflector set up in the French Alps at a site of

superb seeing. His Atlas–Guide Photographique de la Lune, published in 1986,

contains over 200 plates, with technical details and some descriptions of

the surface features.

Most of us have to live with seeing conditions which seldom allow for

sub-arcsecond resolution. Nonetheless, photographically recording images

of the Moon is still a personally rewarding exercise. Attempts to record any

suspected transient phenomena are most certainly of the utmost scientific

value. I hope that you will try your own hand at lunar photography and I

offer the following notes by way of an introduction.

4.1 FILMS FOR LUNAR PHOTOGRAPHY

Of all the film formats on the market, the most common these days is the

35 mm, or 135, as it is properly known. There is a vast array of colour neg-

ative, colour positive and black and white negative films easily available in

the 135 format. Most cameras, particularly most of the highly desirable

single-lens reflex (SLR) cameras, use this film format. So, my recommenda-

tion is to select a camera that uses 35 mm films.

Having settled that, what type of film should we select for our lunar

photography? It is always nice to have colour photographs but that is

4.1 FILMS FOR LUNAR PHOTOGRAPHY 71

hardly essential in the case of the Moon. Even better if we can give slide

shows of our photographs, though colour prints are sometimes more con-

venient. Certainly they are more portable than a slide projector and screen.

However, it is now easy and fairly inexpensive to get prints run off from

colour positive (�‘transparency’, also known as ‘slide’) films.

Films come in different sensitivities, or speed ratings. Surely light

is almost always at a premium in astronomical photography, so a ‘fast’

(�sensitive) film is desirable?

Is that it, then? We need a fast colour transparency film, from which we

can order a set of prints if desired as well as having them mounted as

slides? Unfortunately, things are not that straightforward if we wish to get

the best possible results. Take a look at Figure 4.1, first viewing it from a

distance and then up close. It is a print I made from a fast colour transpa-

rency film. The horrible ‘pebbledash’ effect is known as photographic grain.

Obviously it limits the amount of detail that can be shown. Prominent

grain is an unfortunate characteristic of fast films. ‘Slower’ (�less sensi-

tive) films have a much finer grain structure and allow finer details to be

resolved (grain size is not the only factor which determines a film’s resolu-

tion of detail but it is an important one).

The film speed is quoted as an ISO (International Standards Organisa-

tion) number. The number is in two parts, the first corresponding to the

arithmetic ASA number that most modern photographers are familiar

with and the second a logarithmic value, equivalent to the old DIN

number. For instance Ilford’s FP4 black and white negative film has a speed

of ISO 125/22°. In this book I propose only referring to the arithmetic part

of the ISO number. Hence a film of ISO 250 is twice as sensitive (twice as

‘fast’) as a film of ISO 125. The ISO 250 film would record an image of half

the brightness in the same exposure time as would the ISO 125 film.

Alternatively, it could record an image of the same brightness in half the

exposure time.

As an aside, I ought to mention that there is an effect called reciprocity

failure, whereby halving the brightness necessitates using more than

double the exposure time. However, this effect only becomes really signifi-

cant for light levels low enough such that exposures of more than several

seconds are needed. We photographers of the Moon need not concern our-

selves too much with reciprocity failure.

Of course, we must not forget that the ISO 250 film will have a poorer

resolution and noticeably larger grain structure in the final photograph.

As far as photographic emulsions are concerned, resolution is expressed in

‘lines per millimetre’. If a grid of fine black lines with white spaces between

were imaged onto the film, then when the film was processed it could only

show the grid if the spacing of the lines were greater than a certain figure.

For instance FP4 film, if processed according to the manufacturer’s instruc-


tions, has a resolving power of 145 lines per millimetre (this is the manu-

facturer’s quoted value). In other words, if the spacing of the lines were less

than 1/145 millimetre the film could not resolve them as separate and a

grey area would be seen instead of the grid of separate black and white

lines. A fast (ISO 1000, or more) film might only resolve about 40 lines per

millimetre. We might not be terribly interested in photographing grids of

4.1 FILMS FOR LUNAR PHOTOGRAPHY 73

Figure 4.1 The deleteriouseffects of photographicgrain.

black and white lines but we are certainly concerned to record the finest

possible details on the Moon.

Another factor we should consider is the levels of contrast we can

expect in our final photographs but I defer a discussion of this until Section

4.6. If we are using a colour film, the accuracy of the colour reproduction

is also of some concern. Not all colour films will give natural looking repro-

ductions of the Moon’s subtle tones. In fact, do we need a colour film at all,

since most people see the Moon as stark blacks, greys and whites, anyway?

After the foregoing generalities it is now time to settle on some specifics.

There are a number of techniques you might employ to image the Moon.

You might be wishing to take the most detailed possible photographs of the

Moon through your telescope. At the other extreme, you might just want to

photograph the phases of the Moon, and possibly eclipses, with a simple

camera mounted on a tripod. In the following notes I detail how you might

go about it and in each case I make suggestions of the specific film types you

might first like to try. My intention, though, is for you to treat my recom-

mendations as only the first step; merely enough to get you started. Once

you gain some practical experience my only advice, then, is that you experi-

ment for yourself and refine your own techniques. Good luck!

4.2 TRIPODS AND TELEPHOTO LENSES, FOCAL RATIOS AND EXPOSURES

If you want to picture the Moon against a particular asterism, or perhaps a

grouping of planets, then you will need a larger field of view than you will

get by imaging through your telescope. Setting the camera on a tripod and

taking photographs using its standard lens, or a telephoto lens, would be

best. Of course, the rub is that the image scale will be such as to reproduce

the Moon at rather small size on the final photograph.

The image scale, I, measured in arcseconds per millimetre, produced by

an optical system of effective focal length F is given by:

I�206 265/F, (4.1)

where F is measured in millimetres. F is the effective focal length because

this takes into account any additional optics, such as teleconverter lenses,

etc. The Moon’s apparent diameter is approximately 2000 arcseconds. This

provides a useful ‘rule of thumb’ in that the diameter of the focused full

Moon is approximately 1/100 of the effective focal length of the optical

system. If we are imaging the Moon at the 2 m focus of a large telescope

then the Moon will appear approximately 20 mm across on the film. If we

use a 200 mm telephoto lens then the Moon will appear just 2 mm across.

With the standard photographic lens of 50 mm focus the Moon’s image

will span only 0.5 mm.

Of course, this is just the size of the Moon on the film. If, for instance, a

print is made from the film, it will be enlarged when printing. However, the


Moon’s image photographed using a standard lens and made into a post-

card-sized print is still going to be less than a couple of millimetres across.

A film frame in the 135 format covers 24 mm�36 mm. Most optical

systems produce images with a degree of geometric distortion. In the case

of camera lenses the image scale almost always gets a little larger (fewer

arcseconds per millimetre) away from the centre of the field of view.

However, the effect is not usually too severe except in the case of wide-angle

(�short focal length) lenses, so it is easy to work out the approximate sky

coverage and size of Moon you can expect. Table 4.1 gives the results for

some standard lens sizes.

The Moon, at least approximately, shares in the diurnal motion of the

stars. True, it lags slightly but it still takes a month to reverse through the

constellations of the zodiac. It can also stray up to 281⁄2° north or south of

the Celestial Equator (where the stars appear to move the fastest) but this

makes only a small difference to its rate of travel across the sky. Unless we

are guiding our camera to follow the Moon we must limit our exposure

times to avoid its image being smeared across the photograph by its

motion. My experience leads me to propose the following formulae for fast

(�low-resolution) and slow (�high-resolution) films:

FAST FILM: Maximum exposure (seconds)�550/F, (4.2)

SLOW FILM: Maximum exposure (seconds)�300/F, (4.3)

where F is the effective focal length of the optical system, measured in

millimetres. Hence with a fast (e.g. ISO 400) film in the camera you could

4.2 TRIPODS AND TELEPHOTO LENSES, FOCAL RATIOS AND EXPOSURES 75

Table 4.1. Image scales and corresponding angular sizes of field covered by a 135

format film frame for lenses of various focal lengths.

Image scale Angular field of film frame

Focal length (mm) (arcseconds/mm) (degrees)

50 4125 27.5�41.3

135 1528 10.2�15.3

200 1031 6.9�10.3

300 688 4.6�6.9

400 516 3.4�5.2

500 413 2.8�4.1

1000 206 1.4�2.1

1500 138 0.92�1.38

2000 103 0.69�1.03

2500 83 0.55�0.83

3000 69 0.46�0.69

use an exposure time of up to 11 seconds with a 50 mm focus lens but

would be limited to no more than 1.1 seconds if you were using a 500 mm

telephoto lens. I summarise some results for various focal lengths in Table

4.2. Some people would argue that I have been too severe and slightly

longer exposures could be given. I am sure that others would say I have

been too lax. What you will find tolerable in practice will be determined by

the quality of your lens, the resolution characteristics of the film you use

and the enlargement to which you subject your photographs.

So much for the length of the longest exposure we can give with a fixed

camera but how long an exposure do we need to give? The answer to that

depends on four main factors: the apparent brightness of the Moon, the

optical transmission efficiency of the optical system, the sensitivity

(‘speed’) of the film, and the effective focal ratio of the imaging system.

The brightness of the Moon varies considerably with its phase, so we

need to worry about the phase of the Moon when deciding on the exposure.

As for the transmission efficiency of the system, that is a factor which is

best allowed for by actually attempting lunar photography. If you get lunar

images dimmer than you expect, well, just increase the length of the expo-

sure! It is, though, unlikely that the efficiency of the system would fall

outside the range 50 per cent to 95 per cent, in which case the end results

ought to be fairly predictable.


Table 4.2. Recommended maximum exposure time for

unguided exposures when photographing the Moon

with lenses of various focal lengths, using ‘fast’ (low-

resolution) and ‘slow’ (high-resolution) films. Of course,

the shortest exposures recommended will, in practice,

necessitate using the closest standard shutter speed

setting on the camera (preferably rounding down).

Recommended

exposure time (seconds)

Focal length (mm) Fast film Slow film

50 11.0 6.0

135 4.1 2.2

200 2.8 1.5

300 1.8 1.0

400 1.4 0.75

500 1.1 0.60

1000 0.55 0.30

A much more important factor is the speed of the film. The manufac-

turer will quote a value but this may be altered by the processing. Often the

manufacturer quotes a range of ISO values with some indication of the

options available for processing. ‘DIY-ers’ can process a photographic film

to a widely different speed rating than that intended by the manufacturer.

More about this in Section 4.6.

The last of the main factors is the effective focal ratio of the system.

Effective focal ratio, f, is given by:

f�F/D, (4.4)

where F�effective focal length and D�aperture. Both quantities must be

expressed in the same units, for example both in millimetres, etc. This

ratio is the same as the ‘f/number’ so familiar to photographers. In the case

of the camera lens, the focal ratio is usually altered by changing the effec-

tive aperture of it by means of an internal iris. Teleconverters inserted

between the camera body and the chosen camera lens are useful in that

they provide different effective focal lengths, and so different image scales.

As an example, a �2 teleconverter doubles the effective focal length of the

lens. Do remember, though, that the doubling of the focal length is

achieved with the same iris opening (�effective aperture), so the effective

focal ratio of the lens is now doubled.

You might think that since the effective aperture of the lens remains

the same it should intercept the same amount of moonlight and so the

exposure we should give should not be altered when we insert the telecon-

verter. Instead, the effective focal ratio is crucial in determining the correct

exposure.

To understand why consider three lenses, each of 25 mm aperture. One

of them has a focal length of 50 mm, and so has a focal ratio of f/2. Another

has a focal length of 100 mm, and so is an f/4 lens. The last has a focal length

of 150 mm, and so is an f/6 lens. The first one produces an image of the

Moon that is approximately 0.5 mm across. The second lens intercepts the

same amount of light as the first but the image of the Moon it produces is

1.0 mm in diameter, twice the diameter and four times the area of the first.

Thus, the surface brightness of the image of the Moon produced by the f/4

lens is only one-quarter of that produced by the f/2 lens. The f/6 lens again

intercepts the same amount of light as either of the other two lenses but

it produces an image of the Moon that is spread to three times the diame-

ter, and so nine times the area, of that produced by the f/2 lens. The f/6 lens

produces an image of the Moon that is only one-ninth as bright, in terms

of the light per unit area in the image, as that produced by the f/2 lens. It

is the brightness per unit area of the image on the film that is important

in determining the correct exposure.


In general for extended (non-point) objects:

required exposure � f 2. (4.5)

Objects which produce point images, such as stars, are not (within limits)

diluted by increasing focal lengths. Consequently, the limiting stellar mag-

nitude obtainable in your photographs is a function of aperture (and, of

course, length of exposure and film sensitivity) but not of effective focal

ratio.

Bearing all the foregoing in mind, I can proffer a table of recommended

exposures at various effective focal ratios (see Table 4.3). To simplify the

table I have standardised the film speed at ISO 125. If you wish to use a film

of higher speed then simply reduce the exposure time in proportion. Use

of a slower film necessitates increasing the exposure time in proportion, of

course.

The figures in the table are based upon my own experiences in lunar

photography using my own equipment. In time you will undoubtedly

replace my figures with your own and I offer them here merely to get you

started. Actually, I recommend that you go one stage further and bracket

your chosen exposure with one of half the value and one of twice the value.

Do this even after you have gained enough experience to be fairly confident

that your chosen exposure should produce acceptable results and you will

guarantee a high success rate in your lunar photography.

Enough of the theorising. Let us now do some photography. We set up

our camera on a firm tripod and decide to use a 200 mm telephoto lens to

photograph the phases of the Moon. We hope to also capture some of the

coarsest of the markings on the Moon’s illuminated disk, particularly the


Table 4.3. Recommended exposure times for photographing the Moon at various

stages of the lunar cycle using various effective focal ratios. These figures have been

standardised for recording onto film of speed ISO 125. These figures can be used to

calculate exposure times for other focal ratios and film speeds. Interpolating will

allow the exposure times needed for other lunar phases to be estimated.

Exposure times (seconds) for each of the

Lunar phasefocal ratios indicated

(days) f/5 f/7 f/10 f/14 f/20 f/28 f/40 f/56 f/80

3 days, 25 days 1/30 1/15 1/8 1⁄4 1⁄2 1 2 4 8

7 days, 21 days 1/125 1/60 1/30 1/15 1/8 1⁄4 1⁄2 1 2

10 days, 19 days 1/250 1/125 1/60 1/30 1/15 1/8 1⁄4 1⁄2 1

15 days (full Moon) 1/1000 1/500 1/250 1/125 1/60 1/30 1/15 1/8 1⁄4

major ‘seas’. What film should we have in the camera? Of all the black and

white films available I have no hesitation in recommending one above all

others; and that is Kodak’s TP2415. Depending how it is processed, it can

have a speed rating of between ISO 25 and ISO 200 with normal develop-

ment techniques (hypersensitisation, by which technique TP2415 can be up-

rated to ISO 1200, is only of interest to ‘deep sky’ astrophotographers) and

a resolution of between 125 and 400 lines per millimetre. This is roughly

double the resolving power of other films of comparable speed. It also pro-

duces good strong contrast but it is the potential resolving power of the

film which really sets it apart from the other black and white films. As far

as colour negative and colour positive (�transparency) films go, they are

much more evenly matched speed for speed.

One thing I would urge is to go for films of fairly low speed ratings, cer-

tainly less than ISO 200. For most telephoto shots you will be using a fairly

low focal ratio, almost certainly less than f/22 even if you include a �2 con-

verter, and so you are best off using a slow (and hence high-resolution) film.

Even then, the exposures will likely be shorter than a second – an exposure

length permissible for an effective focal length of up to 550 mm. You cer-

tainly will not need a fast film to achieve this and since the slower films

have the better resolution characteristics, why use a fast one, anyway?

For colour photography, you might like to try films such as Kodak Gold

100 ( a colour negative film with a speed rating of ISO 100) or Kodachrome

64 (a colour transparency film of speed ISO 64), though the market place is

replete with competing films by other makers.

Colour renditions do vary. Some films tend to make the Moon look

greenish. Others tend to make it look brown. I will leave you to do your own

experimenting and find the colour films that produce results you like best.

As with any conventional photography of earthly subjects, the tripod

and camera must not shake during the exposure. Investing in a good, sturdy

tripod is very important. Another good investment is a cable release for the

camera. It is very difficult to avoid jarring the camera when pressing the

exposure button. Even so, before loading the camera with film it is wise to

check that the mirror-slap inherent in single-lens reflex cameras produces

no visible vibration of the camera perched on its tripod. If you see a visible

twitch then you need to make or buy something very much better. Non-SLR

cameras, or ones which have a lock-up reflex mirror, are naturally much less

troubled by shake during the exposure. Talk to your photographic dealer

and study the current magazines to find out what is available in the market

place at the time you are ready to make the purchase. The Olympus OM1 was

always a firm favourite of astrophotographers of recent years.

As well as recording the phases and the coarsest of the surface details

of the Moon, telephoto shots are particularly suitable for capturing the


beauty of lunar eclipses. Eclipse photography is made complicated by the

vast change in the brightness of the Moon during the event, as the brilliant

full Moon gives way to a coppery-red umbra. Even worse, the darkness of

the umbra can vary from eclipse to eclipse. With a largely cloud-covered

Earth and a patch of good transparency through which you can see the

Moon, the umbra can be a bright golden colour. At the other extreme the

umbra can be dark enough to be invisible to the naked eye. In Table 4.4

I offer some recommended exposure times for eclipse photography.

However, these must be treated as a very rough guide at best. Certainly

bracket your chosen exposures by ones of double and half the values. If

your resources allow, having one camera loaded with slow (ISO 50–100) film

for photographing the partial phase and another loaded with a fast film

(ISO 400–1000) for capturing details in the umbra would be the ideal.

For the same reason that the brightness of the umbra of the eclipsed

Moon is hard to predict, so is the brilliance of Earthshine. Something

around five seconds exposure at f/5 and with an ISO 400 film in the camera

ought to be right. Of course, if you are using a relatively short focal length

camera lens to capture the image, you might be better off with a longer

exposure on a slower film to get the best possible resolution.

The difficulties in photographing the eclipsed Moon and the

Earthshine are both lessened if you are able to photograph at the principal

focus of your telescope (provided its focal length is not too long). This topic

is discussed in the next section.

4.3 LUNAR PHOTOGRAPHY THROUGH THE TELESCOPE – AT THE

PRINCIPAL FOCUS

Some people mean ‘principal focus’ when they incorrectly say ‘prime

focus’. I am willing to wager that amateur reflecting telescopes with no


Table 4.4. Recommended exposure times for lunar eclipse photography. These are

the times for ISO 100–125 film at f/5, ISO 200–250 film at f/7, ISO 400–500 film at

f/10, or ISO 800–1000 film at f/14. The tabulated figures can be used as the basis for

calculating exposure lengths at other focal ratios and film speeds.

Stage of eclipse Exposure time (seconds)

First umbral contact 1/250

Umbra half covering Moon 1/125

Umbra three-quarters covering Moon 1/30

Just before totality 1/15

Just after onset of totality 5

Mid totality (for an average eclipse) 15

secondary mirror and equipment mounted at the true prime focus

position are extremely rare. In most cases the ‘principal focus’ will be

the Newtonian focus, though the first focal plane of the refractor, the

Cassegrain reflector, or the catadioptric telescope also counts. The photo-

graphic emulsion is positioned at the principal focus in each case with no

additional optics to further enlarge the image. The basic principles already

set out in this chapter apply here, equally as well as for conventional photo-

graphic lenses. In effect the telescope becomes the telephoto lens.

Image scale, and so the size of the Moon’s image on the film, are calcu-

lated just as before. Obviously the Moon’s image diameter is likely to be

larger because your telescope’s focal length is probably larger than that of

any of your photographic lenses. If your telescope’s effective focal length is

longer than about 2.4 m, you will find that you will not be able to fit the

entire Moon within the film frame.

As before, the exposure required for a given lunar phase and effective

focal ratio can be derived from Table 4.3. Most telescopes used by amateurs

have ratios somewhere in the range of f/4.5 (for the ‘fastest’ Newtonian

reflectors) to f/20 (for some Cassegrain reflectors), with the greatest number

having ratios in the range f/6–f/15.

The problems encountered with photography at the telescope’s princi-

pal focus are usually ones of pure mechanics. Just mounting the camera at

the correct position can be a headache. Many telescope suppliers provide a

wide range of accessories you can purchase, including ‘T-ring’ adapters

that can fit your lensless camera body into the telescope drawtube.

However, the film-plane within the camera will normally be about 5 cm

back from the T-ring. You might find that the focuser will not rack inwards

far enough to allow the film to reach the focal plane. Making or buying a

low-profile focuser might solve the problem. If not, then you might have to

take the drastic action of altering the positions of the optics of your tele-

scope (for instance with a Newtonian reflector moving both the secondary

mirror and the focuser a little down towards the primary mirror) within

its tube.

Sorry, but I must say it: Do not even think of doing this unless you are

sure you are competent to undertake this task, that you can make all of

your measurements and alterations accurately, and can safely store the

telescope’s optics while carrying out the work. I would hate to think of

any enthusiast ruining their expensive telescope because of anything I

have written, so please forgive me including this elementary warning.

Remember that if you move a reflecting telescope’s secondary mirror a

little towards the primary it will intercept a larger area of the cone of rays

from the primary. Make sure that the secondary mirror is large enough to

still intercept all the rays (see Equation (3.2), Section 3.4). It might work fine

in its original position but could easily vignette the field of view (prevent all

4.3 LUNAR PHOTOGRAPHY THROUGH THE TELESCOPE – AT THE PRINCIPAL FOCUS 81

the rays from the primary reaching the outer parts of the field of view) if

you move it too close to the primary mirror. Vignetting might also be

caused by the telescope drawtube or even the camera’s T-ring for telescopes

of ratio lower than about f/5.

One quick method of checking for obstructions in the light-path is to

set the camera, with no film loaded in it, in the telescope and adjust to

produce a focused image through the viewfinder (assuming here an SLR

camera) as if you were about to make an exposure. Lock open the shutter

on the ‘B’ setting. Then open the back of the camera and let your eye search

the rectangular aperture that defines the film frame. Can you see the

primary mirror/objective of the telescope unobstructed, even with your eye

positioned to correspond with the corners of the film frame? If not, then

the image will be vignetted. You should be able to see what is causing the

vignetting. You might decide to put up with it, especially if the image of

the Moon is small enough on the film frame not to be significantly affected

and only the corners of the film frame are significantly darkened. At least

you will be able to see what component(s) of your telescope is/are causing

the obstruction and so you can make an informed decision whether or not

it is worth making the necessary changes to your telescope.

Does your telescope need to be driven (at least at the sidereal rate, if not

actually at the lunar rate) in order to get sharp photographs? In general,

the answer will be “No” for most of your lunar photography at the princi-

pal focus. The rule of thumb formulae I have given for the longest exposure

times permissible when using a photographic lens are a little too lax to

apply when using your telescope to do the imaging. The reason for this is

that your telescope should have the potential to produce nearly diffraction-

limited images. Most photographic lenses, even good-quality telephoto

lenses, are not this good. Telescopes larger than about 5-inch (127 mm) in

aperture could potentially image details down to about an arcsecond in

extent (this is about 1.7 km at the Moon’s distance). Another limiting factor

comes into play for apertures larger than this: atmospheric turbulence.

This might limit the attainable resolution to 1 or 2 arcseconds on many

nights, however large an aperture you use. Consequently, for ‘principal

focus’ imaging using a 75 mm or larger aperture telescope, of greater than

about 1 metre effective focal length, I would impose a blanket ban on

unguided exposures of longer than 1/15 second duration. Diurnal motion

will smear the Moon’s image by about an arcsecond in 1/15 second. Keeping

the exposure time less than this is usually possible except when using a

slow film with a ‘slow’ telescope to photograph a thin crescent Moon.

Trying to capture the Earthshine or a lunar eclipse almost certainly will

require exposures of several seconds, even with a low focal ratio and a fairly

fast film. This necessitates driving the telescope during the exposure.


An often overlooked difficulty is that telescope shake is much more

likely than diurnal motion to dominate as the cause of blurred pictures

for exposure times in excess of 1/60 second. The mirror-slap of an SLR

camera can cause significant problems, the opto–mechanical system of

the telescope being a wonderfully sensitive detector of vibrations! Some

SLR cameras are on the market with lock-up reflex mirrors. After focus-

ing through the viewfinder in the normal way, the mirror is manually

locked into its ‘up’ position and the exposure is made after a few seconds

have passed in order to allow any vibrations to die down. The camera’s

shutter mechanism can produce some vibration, though not as much as

the mirror-slap. I would say that using a cable release is mandatory for

this type of photography. Fumbling to press a button on the camera while

it quivers on the telescope is hardly conducive to getting sharp photo-

graphs!

Another way of avoiding camera–telescope shake is to install a separate

shutter before the camera. Making sure this shutter is first closed, the

camera shutter is locked open on its ‘B’ setting. After allowing a few

seconds to pass for the inevitable vibrations to die down, the secondary

shutter is then opened for the required exposure time. Finally the camera

shutter is, of course, closed. If the foregoing is a little off-putting, it might

well be the case that your telescope is sufficiently rigid not to be troubled

by camera shake for any of the exposure lengths you need to use. You might

get very good lunar photos without having to worry about shake. Why not

try things out first? If you do get smeared images then you will know why

and then can devise ways around the problem.

For photographing details on the sunlit portion of the Moon I recom-

mend Kodak’s TP2415 if you can make your own black and white prints (cur-

rently in the UK it is expensive to have prints made from black and white

films). Colour films, such as Ektachrome 200 (for transparencies) or Kodak

Gold 200 (for prints) will normally be fast enough for the sunlit portion of

the Moon photographed at the principal focus. Personally, I would always

go for a slower film when the Moon’s brightness and the telescope’s focal

ratio allow the exposure to still be less than 1/60 second.

The beauty of lunar eclipses is well brought out by colour films, though

for recording details in the umbra a faster film may be desirable to keep

the exposure length down to a few seconds. There are plenty of ISO 400

films available in black and white, colour transparency and colour print

types.

My general advice about photographing eclipses and the Earthshine

through a telephoto lens (see the last section) is the same when using a

telescope for photography at the principal focus. Figure 4.2 shows a

splendid photograph of the Earthshine by Martin Mobberley using his

4.3 LUNAR PHOTOGRAPHY THROUGH THE TELESCOPE – AT THE PRINCIPAL FOCUS 83

14-inch (356 mm) reflector at its f/5 Newtonian focus (the instrument is a

Newtonian–Cassegrain convertible). The details are given in the caption

accompanying the photograph.

There are further examples of principal-focus photography, for eclipses,

Earthshine, and other whole-Moon shots in Chapter 1 (Figures 1.3 and 1.7),

Chapter 2 (Figures 2.1–2.5) and Chapter 8 (Figures 8.24(b) and 8.46(d)).

4.4 HIGH-RESOLUTION PHOTOGRAPHY

The image scale at the 2.59 m Newtonian focus of my 181⁄4-inch (0.46 m) tele-

scope is 80 arcseconds per millimetre. In perfect seeing the telescope

should allow details as fine as 0.3 arcsecond to be seen. In order to photo-

graphically record details this small by imaging the principal focus directly

onto the film, the film would have to have a resolution of 260 lines per

millimetre. Of the films commonly available only Kodak’s TP2415 poten-

tially has this resolution if processed in the correct way. Even so, how does

one focus the image to the necessary degree of precision? The camera view-

finder (here assuming an SLR camera) will not be good enough. Granted,

the chances of getting seeing that good are remote on any given night,

anyway, but that is no reason to forego trying to get the best resolution pos-

sible in your lunar photographs. The inescapable conclusion is that to have

the best chance of recording lunar images of the highest resolution pos-

sible on the greatest number of nights possible one must enlarge the

primary image. There are four main methods of doing this: projection

using a Barlow lens, projection using an eyepiece, relay lens projection,


Figure 4.2 Earthshine onthe Moon, photographed by Martin Mobberley at the f/5 Newtonian focus ofhis 14-inch (356 mm)reflecting telescope on 1989 August 28d 03h 20m UT.The 5 second exposure wasmade on T-Max 400 film.

and infinity-to-infinity (� to �) focusing using the eyepiece and camera

lens. The following notes detail each of these methods.

Barlow projectionFigure 4.3 shows the arrangement, together with the formulae for

working out the enlargement factor. The lens must be mounted into a

tube with the appropriate bayonet or screw-fitting attachment to your

camera. The only real problem with Barlow lenses is that they are usually

designed for one specific value of amplification (commonly �2). Using

them to provide any other value of amplification necessarily increases the

aberrations produced by the lens. This lowly amplification may not be

enough to match the potential resolution of the telescope to that of the

film. At the time of writing (summer 1998) there is one high-quality

Barlow lens commercially available, Tele Vue’s ‘5x Powermate’, which you

4.4 HIGH-RESOLUTION PHOTOGRAPHY 85

Figure 4.3 The opticalconfiguration for project-ing (and enlarging) theprimary image by meansof a Barlow lens.Alternative formulae aregiven for calculating theamplification factor, a. Thefocal length of the Barlowlens is F. It is entered inthe equation as a negativequantity.

u

v

a = – va = – u

a = v 1 – 1a = v (u – F)

could use for your photographic work. Unscrewing the lower section of the

unit, containing the four-element lens itself, (and remounting it in your

own tube with an adapter to your camera) would work but make sure that

the lens–film distance is pretty much the same as the manufacturer’s

intended lens–eyepiece distance. The amplification will then be close to

the manufacturer’s intended �5 and the performance of the lens will be

good. Let me emphasise one important point: Unscrew the barrel con-

taining the lens in its cell by all means but do not even think of disturb-

ing the lens assembly in its mounting unless you are an optical

specialist – you could so easily ruin the performance of this expensive

accessory it is just not worth taking the risk.

Another reason for keeping to the manufacturer’s intended amplifica-

tion factor when using a Barlow lens is the possibility of introducing

some vignetting if you do not. In the severest case you might be unknow-

ingly stopping the telescope down to a small aperture! The minimum

diameter, D, the Barlow lens should be in order to fully illuminate the

projected image out to a diameter, d, centred on the optical axis is given

by:

D� , (4.6)

where a is the amplification factor, v is the distance the lens is set inside

the telescope’s focus, and f is the focal ratio of the telescope without the

Barlow in position.

As an example of Barlow amplification in action, using the 5x Powermate

to project the image from a 12-inch (305 mm) f/5 Newtonian reflector onto

the film, at the manufacturer’s intended amplification factor, produces an

effective focal length of 7625 mm, an effective focal ratio of f/25 and an

image scale of 27 arcseconds per millimetre. The potential, diffraction-

limited, resolution of the telescope is 0.45 arcsecond. To realise this would

require a film resolution of at the very least 60 lines per millimetre. This

scale will produce a Moon of about 7.6 cm diameter, only a portion of which

will fit within the film frame in one go.

Eyepiece projectionAs Figure 4.4 shows, the eyepiece is mounted so that the rays emerging

from the eyelens converge to form a focused image on the film.

Unfortunately, this is not what the eyepiece was designed to do. Sets of par-

allel rays emerge from the eyelens and enter the observer’s eye when the

eyepiece is used as the manufacturer intended. Using it as a projection lens

involves setting it slightly further out from its normal focused position in


D� ,1

a �vf �d�

the telescope, which is usually not a problem. Unfortunately, the result is

an increase in the optical aberrations produced by it. Good eyepieces will

still produce sharp images within a small area of the centre of the film

frame but the outer zones can be very blurred.

Figure 4.5 shows one of my early attempts at eyepiece projection

photography. Notice the horrendous outfield blurring I got using an 18 mm

Orthoscopic eyepiece to enlarge the f/5.6 Newtonian focus of my 181⁄4-inch

reflector to f/17. This problem is greatly reduced when using the eyepiece

to create larger amplification factors. The reasons for this are two-fold.

Firstly, the rays emerging from the eyelens are less convergent (and so the

paths of rays through the eyepiece are nearer to what the manufacturer

intended). Also, the ‘sweet spot’ of a sharply focused image on the film is

increased in size by virtue of the greater magnification, anyway.

For lower amplification factors a high-quality Barlow lens may serve

best. Eyepiece projection would be the best choice for large amplification

factors. Figure 4.6 shows a good example of the results obtainable by this


Figure 4.4 The opticalarrangement for enlargingthe primary image by eye-piece projection. Theamplification factor, a, isfound from the equationgiven. The focal length ofthe eyepiece is F. The equa-tion is approximate asexplained in the text.

va = v – 1a = (F )

technique. You will find others in Chapter 8 (Figures 8.5(c), 8.13(a), 8.13(f),

8.14(a), 8.17(a), 8.17(b), 8.24(a), 8.26(a), 8.26(b), 8.30(a), 8.34(a), 8.35(a), 8.42(a),

and 8.44(a). All details are given in the accompanying captions. You will

gather that eyepiece projection is the most popular method of primary

image enlargement!

Relay-lens projectionThe aberrations, particularly outfield blurring, inherent in using eye-

pieces to project the primary image are avoided if one can use a relay lens,

or other type of compound lens specifically designed for projection. The

lens from a photographic enlarger would be a good choice. Some camera

lenses might also be suitable. The principle is easy. As always, the diffi-

culty is actually constructing the mechanical supports/adapters/tube-

work/etc. to do the job. There are as many solutions as there are different

telescopes. What you can do really depends upon your own construc-

tional skills and the materials and tools you have available. Remember,

some or all of the parts you need might be obtainable ready-made from

telescope manufacturers/dealers and/or photographic dealers/manufac-

turers. While always urging great care with your expensive camera and


Figure 4.5 The horrendousblurring of the outer zonesof this photograph is asevere disadvantage of themethod of eyepiece projec-tion when used to providelow amplification factorsto image the Moon. Thisphotograph was taken bythe author on 1977September 2d 23h 57m UT.He used an 18 mmOrthoscopic eyepiece toenlarge the f/5.6 primaryimage of his 181⁄4-inch(0.46 m) Newtonianreflector to f/17. The expo-sure was 1/30 second,made on Ilford Pan F blackand white film.

telescope, I certainly advocate an experimental approach to your practi-

cal astronomy.

To avoid effectively stopping-down the telescope, the focal ratio of your

relay lens should be no more that one-half that of your telescope. At least

that is the case for fully illuminating the centre of the field of view with

the amplification factor being unity. The equation for predicting the

amplification factor is the same as that for eyepiece projection. Though the

focal ratio of the lens can be a little higher when used to produce greater

amplification factors, this might still only fully illuminate the very centre

of the field. Keeping the focal ratio to no more than one-half that of your

telescope for higher amplification factors would then increase the size of

the unvignetted area on the film.

Under this heading I include the commercially produced teleconverters

and tele-extenders, which can work excellently with telescopes, even if they

are designed to be used between a camera body and a conventional photo-

graphic lens.

Infinity-to-infinity focusing, using the camera lens and the eyepieceThough the purist might shudder at the thought of eight or more separate

lens elements between the principal focus and the film, and have night-

mares about multiple reflections and a ‘fog’ of light swamping the dim

image, keeping both the telescope eyepiece and the camera’s lens in place

can actually work really well. With today’s multicoated eyepieces and

camera lenses the amounts of light scattered, reflected, and absorbed by


Figure 4.6 The intriguinglunar crater Schiller, pho-tographed by MartinMobberley on 1984 March14d 20h 55m UT. He usedeyepiece projection toamplify the f/20Cassegrain focus of his 14-inch (356 mm) reflector tof/60. The 1⁄2-second expo-sure was made on IlfordXP1 black and white nega-tive film. Schiller is orien-tated with its long axisroughly north–south onthe Moon, though in thetelescope field south liesapproximately to theupper left (Schiller liesclose to the Moon’s south-east limb).

them are very much more reduced than was the case for the products of

yesteryear.

In this arrangement the eyepiece is focused in the normal way and then

the camera, complete with its lens set to � (infinity) focus, is brought up to

the eyepiece. The camera is carefully positioned such that it looks squarely,

and on-axis, into the eyepiece. In effect, the camera has replaced the

observer’s eye.

This technique can work with a non-SLR camera, though having the

facility to see what the camera is seeing is certainly an aid. Also, some

tweaking of the focusing can be made if you use an SLR camera. Given that

there might be some uncertainty in the precise ‘infinity’ focus of your eye

caused by the natural accommodation of focus and/or any long- or short-

sightedness, one can expect better and more consistent results by directly

viewing through the camera’s focusing screen.

However, the modern low-cost ‘point and shoot’ cameras are unlikely to

produce any worthwhile results. They are set up for photographing sub-

jects such as Aunt Matilda patting your pet Rottweiler in your garden; and

the flash gun is certainly not powerful enough to be of any use in your

lunar photography! By all means do try but be prepared for disappoint-

ment.

The amplification factor, a, is given simply by the ratio of the focal

lengths of the camera lens, Fc, and eyepiece, Fe:

a�Fc /Fe. (4.7)

Figure 4.7 shows a photograph of the Moon I took using this method.

One advantage of this method is that both eyepiece and camera lens are

being used well within their intended parameters and so can deliver

images of the highest quality. You might notice that Figures 4.5 and 4.7 are

both taken at the same effective focal ratio. Also, they are both virtually

full-frame reproductions from the negative. The much more even focus of

Figure 4.7 is obvious.

While it is always best to firmly attach the camera to the telescope,

another advantage of the infinity-to-infinity method is that tolerable

results, though certainly not the best results, can be obtained by hand-

holding the camera to the eyepiece and taking a ‘snapshot’! I took Figure

4.7 exactly that way. I often use this method when I want to take quick

photographs without going to the trouble of setting up the equipment to

attach the camera to the telescope. Figures 8.20(a) and (b), also 8.34(b),

further on in this book, were taken by the same method. Details of the film

used, effective focal ratio in each case, etc., are given in the accompanying

captions.

Of course, hand-holding the camera demands that the exposures


should certainly be shorter than 1/30 second, better 1/60 second or less, if

consistently sharp photographs are to be obtained.

The ‘rub’ is that exposures that short demand a fast (and hence grainy

and low-resolution) film in the camera. Even then the amplification factor

cannot be too high. However, using this technique it is possible to photo-

graph terminator details in the first or the last quarter Moon with an


Figure 4.7 The authorused the ‘infinity-to-infinity’ method to obtainthis view of the southernhighlands of the Moon on 1987 January 7d 19h 20m UT. The camera, fitted with astandard lens of 58 mmfocal length, was hand-held to an 18 mmOrthoscopic eyepieceplugged into his 181⁄4-inch(0.46 m) Newtonianreflector. The EFR of thisarrangement is f/17, thesame as that for the photo-graph shown in Figure 4.5.Notice the much moreeven focus achieved by the‘infinity-to-infinity’method. The film used was3M Colourslide 1000 andwas commerciallyprocessed, though theauthor subsequentlycopied the transparencyonto black and white nega-tive film so that he couldmake his own print.

exposure of 1/60 second on ISO 1000 film at an effective focal ratio of no

higher than about f/20. A typical ISO 1000 transparency film, such as 3M’s

Colourslide 1000, will likely have a resolution of about 40 lines per milli-

metre. With a 12-inch (305 mm) telescope you might just be able to capture

details at the arcsecond level of resolution at f/20 using Colourslide

1000 (the image scale being 34 arcseconds per millimetre on the film).

Obviously, the chances of recording fine details get much better nearer full

Moon (when a slower film and/or a shorter exposure and/or a greater

amplification factor) can be used.

If you feel that attaching your camera to your telescope and arranging

to project the image onto the film is just too much like hard work, then I

urge you to try some hand-held ‘snapshots’ using the infinity to infinity

technique. Your results will be much inferior to the best that could be

obtained but provided you use a fast film in the camera you may be sur-

prised at just how good your lunar photos will turn out. Go on – have a go!

You might even be spurred on to more serious efforts afterwards.

4.5 SLOW FILMS AND LARGE EFFECTIVE FOCAL RATIOS

The simple sums detailed in the foregoing sections predict that one should

be able to achieve arcsecond, perhaps even sub-arcsecond, imaging in your

photography with focal ratios of no higher than f/20, even with a fast film

in the camera. At least this should be the case for the large-aperture end of

the amateur size range of telescopes. However, the best photographs I have

seen of the Moon have all been made using relatively slow films (under ISO

200) with telescopes working at high effective focal ratios (f/40, or more)

and relatively long (circa 1⁄2 second) exposure times.

Problems with camera–telescope shake can become acute with these

long exposure times, even if your set-up is good enough to produce smear-

free pictures at 1/30 second exposure, or less. Failing a commercially

made second shutter inserted before the camera, as mentioned earlier,

you might be able to make something for yourself. A spring-, or motor-

driven rotating blade is a feasible solution. Absolute accuracy in the

timing is not essential but the exposure times produced by your arrange-

ment must at least be reasonably consistent. One ‘low-tech’ approach is

to hold a large black-painted piece of cardboard, shaped like a large

paddle, in front of the telescope as the second shutter. A ‘slicing’ action

will reduce the amount of air turbulence generated in the light-path.

Obviously, short exposures are a problem for this method but 1⁄2 second

should be achievable.

Driving the telescope is mandatory when using longer exposure times.

Even if the drive works smoothly, one should be aware that the Moon

moves across the sky about 4 per cent more slowly than the diurnal


motion. The telescope drive will probably work at the sidereal rate. It also

changes its declination particularly rapidly when close to the Celestial

Equator (the rate of change then being 0.3 arcsecond per second). At these

times the total differential motion is nearly 1 arcsecond per second. Unless

your telescope has a ‘lunar rate’ drive you will be advised to keep your expo-

sures to no longer than 1⁄2 second.

Another difficulty is that the cyclic distortions of the image produced

by atmospheric turbulence may smear the details in image while the expo-

sure is being made. Keeping the length of the exposure down at least pro-

vides the chance of securing a sharp image. Longer exposures are the

preserve of the very best nights. Even then, I would urge taking several

repeated exposures (at each of your chosen bracketed exposure values) in

order to have a fighting chance of getting that one good photograph.

4.6 PROCESSING THE FILM AND TECHNIQUES TO BRING OUT DETAIL IN

PRINTING

Doing the processing/printing yourself is advantageous in that you can

control all that goes on. Tailoring what you do to the subject matter in

hand will potentially give the best results. On the downside, photographic

darkroom work is a hobby all on its own. Setting up a darkroom is expen-

sive, and can be problematical in many homes. Some practice will be

required to master the basics, let alone the more advanced techniques. I

was lucky in that I began photography as a hobby, along with the sciences

– particularly chemistry and astronomy, at a very young age. As the years

progressed I was able to use photography in my astronomical work and

even the chemistry helped in the concocting of various processing solu-

tions with specialised characteristics.

In writing these words, I recognise that very few readers will have any

experience of darkroom techniques. Neither will they have any inclination

to go to the expense and trouble required to set up a darkroom and process

their own photographs. I would go even further and say that the number

of youngsters taking up darkroom work as a hobby is declining – and it is

the young who form the chief intake of hobbyists. This is also true of many

other practical/constructional hobbies. For instance, in the field of astron-

omy there are now very few young people who are even the slightest bit

interested in building their own telescopes and/or auxiliary equipment. I

find this sad but have to recognise this fact in writing this book for the

modern amateur astronomer.

Consequently, later in this section I offer a few brief notes that may help

those who already have some darkroom experience and wish to produce

their own lunar photographs. Most readers will be in the hands of commer-

cial processors and so a few words on that score may first be in order.

4.6 PROCESSING THE FILM AND TECHNIQUES TO BRING OUT DETAIL IN PRINTING 93

Commercial processing of your photographsThe golden rule when having your astronomical photographs commer-

cially processed is to include a note with the film, briefly explaining what

the subject of the film is. If you have any specific instructions (for instance,

“I know these negatives will come out thin, so please up-rate the film to

increase the contrast. Also, when printing please try to avoid the prints

being too dark”) these can be included in your note, though production-

line methods will not allow the processing operative much leeway.

If your photographs include a lot of blank sky (for instance, a sequence

of eclipse photographs taken with a telephoto lens) then include at least

one ordinary (Aunt Matilda in the garden) photograph so that the operator

has something to set the film cutter by. It would be a great shame if you get

your photographs back only to find that your Moon images have all been

sliced in two!

Having your films/photographs processed by a professional photo-

graphic studio/laboratory will allow you to specify a wider range of controls

(second only to doing the processing yourself) but will be verymuch more

expensive.

Processing your photographs yourselfBasic knowledge and experience of darkroom techniques is assumed here.

If you do not have this experience but wish to know what is involved (with

a view to deciding if you do wish to undertake your own processing) please

refer to one of the many books currently available on this subject.

As referred to earlier, the graininess, contrast, and actual photo-

graphic ‘speed’ of a film is dependent on how it is processed. The choice

of developer, the chosen solution strength used, the temperature, and the

development time are all variables that will have a bearing on the final

results.

Generally, extending the development time and increasing the temper-

ature of the solution from the manufacturer’s recommended values will,

up to a point, increase the speed, contrast and graininess of the images on

the film. Go too far, though, and your images will begin to suffer from dich-

roic (chemical) fog. Keeping the other variables the same, reducing the

strength of the developer will reduce the effective speed of the film and the

contrast level in the image.

By experimenting with the dilution and temperature of the developer

along with increasing the development time you may well suppress the

grain. I advocate experimentation. However, I must say that you will prob-

ably get the best results by sticking fairly close to the manufacturer’s

guidelines. When processing my own Moon photographs I tend to process

them at the recommended temperature and solution strength and choose


the development time that corresponds to the high-contrast end of the

range.

As far as printing goes, the Moon does present one difficulty. Whereas

the dynamic range (range of brightness values recordable) of the film

might be of the order of 1000:1, that of the print will be only about 50:1.

Consequently, getting details in the region of the Moon’s terminator while

avoiding the areas away from the terminator being bleached out white is

not easy. Printing onto a low-contrast paper (and/or using a low-contrast

print developer) would certainly compress the tonal values and show a

greater brightness range on the final photograph. However the individual

details will be less well seen and the print will look very ‘flat’. Figure 4.8(a)

shows an example. Figure 4.8(b) shows the result of printing the same neg-

ative onto a high-contrast paper. Note the loss of detail in the regions away

from the terminator.

There is one solution to this problem: use a high-contrast paper (and/or

print developer) but expose different parts of the photographic paper by

different amounts in order to even out the differences in brightness. If you

are experienced in the darkroom you will probably already be aware of this

technique, termed dodging. Figure 4.8(c) shows the result. A piece of card-

board was used as a mask to cover all of the photographic paper, above the

easel, just before the enlarger was switched on. Then the cardboard mask

was slowly withdrawn, uncovering the darkest (on the negative) part of the

image first. The mask was continuously withdrawn over the next few

seconds, until all the photographic paper was exposed to the image. A few

more seconds to complete the exposure and then the enlarger was

switched off. The paper was then developed in the normal way. As always,

a little experimentation will prove invaluable but the improvement in the

results certainly make it worth the effort.

4.7 PHOTOGRAPHY THROUGH COLOURED FILTERS

Though coloured filters can be used in combination with coloured films,

you would normally wish to use them in conjunction with black and white

films. The film that would be the best choice in other respects, Kodak’s

TP2415, is also the best to choose for filter work, owing to its broad spectral

response. TP2415 maintains its sensitivity well into the red part of the spec-

trum. Most other films have poor responses to red light. As it is, using

coloured filters necessitates increasing the lengths of exposures.

The Moon may look monochrome to you but you will be surprised at

the result if you take comparative photographs through red and through

blue filters. A yellow or an orange filter may help improve the contrast of

the image when the sky is hazy. Any residual secondary spectrum pro-

duced by your telescope’s optical system (including the auxiliary optics)

4.7 PHOTOGRAPHY THROUGH COLOURED FILTERS 95


Figure 4.8 One problem peculiar to photographing theMoon is coping with the large brightness variation in thevicinity of the lunar terminator. Each of these prints arefrom the same negative obtained in the same way (date,film and method) as the photograph shown in Figure 4.7.(a) Normal print onto Grade 2 (normal contrast) paper.Most of the details are visible but the result is rather‘washed out’. (b) Print made on Grade 4 (hard contrast)paper. Though some details are much better seen, detailsin the brightest and the darkest regions are lost. (c) Printmade in the same way as (b) but using a moving maskwhile the photographic paper was being exposed underthe enlarger to even out the large-scale image density.

(a)

(b) (c)

can be suppressed by using a strongly coloured filter. A deep-yellow filter

may well be mandatory when using a refractor for Moon photography for

this reason.

4.8 FURTHER READING

My intention in this chapter is to provide enough information to enable

you, the reader, to decide whether or not you would like to try your hand

at photographing the Moon. The notes I have given here should be enough

to get you started if you do decide to have a go. I realise that I have only

scratched the surface, so to speak. I have provided a fuller account of the

methods, techniques and equipment needed for amateur astrophoto-

graphy in my book Advanced Amateur Astronomy. Going beyond that, there

are a few specialist books you might like to consult. I especially recom-

mend: Astrophotography for the Amateur, by M. Covington (Cambridge

University Press, revised edition, 1991); A Manual of Advanced Celestial

Photography, by B. Wallis, and R. Provin (Cambridge University Press, 1988);

and High Resolution Astrophotography, by J. Dragesco (Cambridge University

Press, 1995).

4.8 FURTHER READING 97

Moonshine and chips

Growing numbers of amateur astronomers are following the lead of the

professionals and are now recording images of astronomical bodies in elec-

tronic media. However, not everybody is able to afford the cost of the equip-

ment needed. There will also be many who do not wish to get involved in

the complicated technical matters that are a necessary part of the imaging

process. There is no shame attached to either case. At least I hope not, as

my own astronomy has always had to be done on a shoestring budget and

I do not yet own a ‘proper’ CCD astrocamera. You might lack a large and

expensive telescope, fitted with an expensive CCD astrocamera, linked to

an expensive computer but you are certainly not barred from enjoying

the Moon’s spectacular vistas and studying its physical and topographic

features!

You can still do some useful research (the opportunities for which are

limited, anyway) using ‘old-fashioned’ methods with modest equipment.

However, it is folly to deny that electronic imaging, particularly when

allied to computer processing, permits a significant improvement in the

level of detail attainable. If you can afford it, and if you are happy with

dealing with the technology (particularly computers) involved, then I

strongly recommend that you pursue this field. In the same way as I

intended for the previous chapter on ‘old-fashioned’ photography. I hope

the notes I give in this one should be of help in getting you started if you

do decide to undertake electronic recording of the Moon’s image.

Actually, there is one way of getting very high quality images of the

Moon for a much smaller budget than that needed to set up for ‘full-

blown’ CCD astrophotography: use a domestic video camera to do the

recording. This method is also technically the simplest – you can get great

results without going anywhere near a computer. There are even some

advantages to the video technique which are not shared by other methods.

99

CHAPTER 5

Consequently, I have devoted a large amount of room in this chapter to

video techniques. First, though, let us consider the more usual form of

CCD camera and its operation.

5.1 SOME BASIC PRINCIPLES OF CCD ASTROCAMERAS

A CCD, or Charge-Coupled Device, consists of an array of light-collecting units,

called pixels. Each pixel is usually of a size ranging from 10 �m to 25 �m (10

micrometres to 25 micrometres). Professional astronomers mostly use

large CCDs, typically having 2048�2048 pixels. These are very expensive

and, moreover, make heavy demands on the computer used for the record-

ing and subsequent image processing. Currently, amateurs use smaller

versions. A typical amateur’s CCD might be composed of an array of some-

thing like 500�360 pixels, each pixel being about 15 �m square. The

recordable picture area would be 7.5 mm�5.4 mm in that case.

These figures are only intended to give you an idea of what is typical at

the time of writing (1998). As I write these words, personal computers are

coming onto the market with ever-increasing speed and memory capacity

and sophistication of software. This potentially allows the images gener-

ated by larger CCDs to be processed. I imagine that affordable astrocame-

ras with larger CCDs will appear in the amateur marketplace in the next

few years. It is inevitable that much of the information I provide in this

chapter will be out of date by the time this book appears in print, such is

the current rate of progress in this field. You should bear this in mind and

seek out the latest information if you choose to enter the arena of elec-

tronic imaging yourself. The basic principles will, though, remain stan-

dard for years to come and it is these I offer herewith.

Whatever the size of CCD, the array of pixels are mounted on an ‘inte-

grated circuit’ or ‘silicon chip’ type base which has about 20 individual

electrical connections to its supporting electronics. The way it works is that

photons of light falling on particular pixels liberate electrical charges

within each of them (the energy of the incoming photons causes elec-

tron–hole pairs to be created within the semiconductor lattice). The more

light (and so more photons) falling on a given pixel, the more electrical

charge is created within it. If an image is focused on the picture-receiving

area of the CCD the pixels corresponding to the brightest parts of the image

have the greatest amounts of charge liberated in them. The dimmest parts

of the image generate the smallest amount of charges in the correspond-

ing pixels.

Of course, charges would continue to build up all the while the light is

falling, until each pixels is full, or saturated. Well before this stage is

reached, the process, known as integration, has to be stopped. Ideally an inte-

gration time (equivalent to the photographic ‘exposure length’) is selected

100 MOONSHINE AND CHIPS

so that at the end of it the pixels associated with the dimmest parts of the

image have only a small charge while those associated with the brightest

parts of the image have lots of charge, though less than the amount neces-

sary for saturation.

When the integration is completed the array of charges are sequentially

read off the chip and sent as a representative data stream to a computer,

or other electronics, to deal with in order to recreate the image on a

monitor/TV screen, or to download it into a computer’s memory, or onto a

computer disk, etc.

Photographic emulsions generally have values of detector quantum effi-

ciency (DQE) of about 1 or 2 per cent. In other words, about one in a hundred

to two in a hundred of the incoming photons are detected and go toward

forming the image. The other ninety-eight or ninety-nine of each hundred

photons are wasted. Of course, a DQE of 100 per cent is the best that one

could possibly have; all the incoming photons then being detected. One of

the advantages of the CCDs is that they have DQE values often exceeding

50 per cent. At least that is the case over a limited range of wavelengths.

The earlier examples of CCDs tended to have their maximum sensitiv-

ity in the red, or even the near infrared, portion of the spectrum. A typical

response might be a DQE of about 40–80 per cent in the 600–950 nm wave-

length range falling away steeply at shorter and longer wavelengths to

become zero at about 400 nm and again at at about 1100 nm. This is very

different to the spectral response of the eye, the maximum response of

which occurs at a wavelength of about 550 nm in the yellow-green portion

of the spectrum and falls to zero at about 380 nm (violet) and at about

700 nm (deep red).

Many of the latest generation of CCDs have coatings which enhance

their response to light at the blue end of the spectrum. As an example, the

Philips FT 12 has a response which is closer to that of the human eye. It has

a peak sensitivity at 530 nm, falling to half that value at about 400 nm and

700 nm. However, it does so at the expense of some of its sensitivity, having

a peak value of DQE of only 30 per cent.

Those who wish to image faint comets, nebulae and galaxies will need

a high-DQE chip but there is usually plenty of light available from the

Moon and so DQE is only of minor importance to the lunar imager.

So much for the basic principles. There are a number of variations in

the design of modern CCD detectors. Look at the literature and you will

come across the terms interline transfer and frame transfer. These refer to the

way the image is read off the chip. You will also come across back-illuminated

and front-illuminated CCDs. These terms refer to the mechanical structure

of the CCD. Each type has its theoretical advantages and disadvantages

(mainly in sensitivity, freedom from ‘noise’, resolution and spectral

5.1 SOME BASIC PRINCIPLES OF CCD ASTROCAMERAS 101

response), though as better and better CCDs are manufactured the seeming

advantages of one type tend to be overtaken by those of the other.

One problem afflicting CCDs of all types is something inaccurately

called dark current. While an integration is in progress, thermally liberated

charges build up in each of the pixels. At room temperature these charges

can build up to fully saturate each pixel in just a few seconds. Even before

then the charges are reducing the total dynamic range (range of brightness

levels) recordable. The effects are negligible for very short integration

times, say a small fraction of a second, but integrations longer than that

demand the CCD be cooled. Practical CCD astrocameras have built-in

thermoelectric coolers. This is essential for astronomers wishing to image

faint objects and is desirable, though not essential, for those wishing to

image the Moon or the bright planets.

Limiting ourselves to the requirements of the Moon observer, the basic

characteristics we need to worry about in selecting a suitable CCD astro-

camera are: cost, the size of the imaging area of the CCD (one-half of the

area of the frame-transfer CCD is for imaging, the other acting as a storage

area of the charges before they read off) and resolution in the image

(number of pixels height�number of pixels width comprising the image).

When you are buying a motor car you will be interested in the perfor-

mance figures of the engine. Unless you have a particular interest in car

mechanics you will not trouble yourself with the details of how the manu-

facturer has achieved that stated performance. I expect most readers of this

book will only be interested in the performance figures of the CCD camera,

so I will not waste space and bog things down with further technical theory

here. I have provided details of the more general uses of CCD cameras in

my book Advanced Amateur Astronomy. Here I will concentrate on the matters

of most relevance to the lunar observer.

5.2 CCD ASTROCAMERAS IN PRACTICE

Figure 5.1(a) shows the camera head of the Starlight Xpress SXL8 unit. Notice

the cooling fins projecting from the back of it. The major part of the mass

of the camera head (about 1 kilogram) is associated with the cooling unit.

The small grey square that lies within the head is the actual CCD. It is the

Philips FT12, referred to earlier.

Figure 5.1(b) shows the rest of the Starlight Xpress SX system. It is fairly

typical of commercial units. The plug at the end of the ribbon cable is for

attaching to the user port of the computer. Notice that the camera head

has a short barrel fitted into the front of it. This is so the camera head can

be plugged into the telescope drawtube (or adapter tube if one is using a

Barlow lens, a relay lens, or an eyepiece to enlarge the primary image) in

the same manner as one would plug in an eyepiece. In practice, the weight


of the camera head necessitates re-balancing the telescope tube, perhaps

using counterweights.

Another Starlight Xpress system is shown in Figure 5.2. This one, the SFX

camera system, is unusual in that it is a ‘stand alone’ unit that does not

require the addition of a computer. The box of electronics will capture and

display the images on a monitor direct, though a computer is needed to

save and to process them.

The SXL8 unit is more typical of commercial CCD astrocamera systems.

As well as the Starlight Xpressunits manufactured by FDE Ltd, there are many

others. I recommend searching them out in advertisements in astronomy

magazines current at the time you decide to purchase the camera. Get

further information direct from the manufacturers and take the time to

make your choice carefully. To get you started I have included a limited list

of CCD equipment suppliers in Section 5.6 – but beware; there are many

others and the list only covers some of the main companies trading at the

time of writing.

When you have made your purchase read the manufacturer’s instruc-

tions very carefully. The time and effort spent will be more than repaid by

how quickly you will be able to achieve first-class results. Here I confine

myself to offering a few general comments on matters relating to operat-

ing the camera with your telescope.

In use, you can expect the temperature of the CCD to stabilise in about

10–15 minutes after switching on the cooling unit. The temperature will be

monitored and displayed by the supporting electronics unit as shown in

Figures 5.1(b) and 5.2. After plugging the camera head into your telescope

(with any necessary auxiliary optics in place) the next task is to point the

5.2 CCD ASTROCAMERAS IN PRACTICE 103

Figure 5.1 (a) The StarlightXpress SXL8 camera head.The CCD can be seenwithin it. (The scale is incms.)(b) The complete StarlightXpress SX camera system,typical of commercialunits.

(a) (b)

telescope to the Moon. The small area of the CCD makes this a little diffi-

cult, especially when the primary image is enlarged.

Obviously a finderscope is of help here, especially one fitted with cross-

wires. However, a finderscope is certainly not an essential. Sighting up the

telescope tube will get you pretty close to start with. You will find that on

peering into the telescope tube you can see the patch of moonlight on the

tube wall, the optics, or the internal fittings, and simply move the telescope

until the light drops into the drawtube. Fine adjustment of the telescope’s

aim is achieved by operating the camera and seeing the results displayed

on the monitor.

With the camera plugged into the telescope and it trained on the target

the next task is to focus the image. This is achieved by tweaking the focuser

between exposures and monitoring the results. (Hint – After doing this for

the first time, a mark made using a felt-tip pen, etc. could be put on the

drawtube, or focuser wheel, etc. to speed things up in future.) A motorised

focuser would make life very much easier, allowing all the adjustments to

be done by remote control while you are seated in front of the monitor. If

you cannot afford one, perhaps you can make your own, or even motorise

the existing one?

Of course, tweaking the focus, then performing an integration, waiting

for the image to appear, then tweaking the focus again, etc. could certainly

be time-consuming. However, many astrocamera systems have a special

‘focusing mode’ whereby only a small area near the middle of the frame is

imaged to speed up downloading the images. It produces a rapid sequence

of images, allowing one to quickly achieve the sharpest possible focus.


Figure 5.2 The StarlightXpress SFX system isunusual in that it cancapture and displayimages without the needfor a computer. Saving andprocessing images does,though, require a com-puter.

The procedures for making dark frame and flat field exposures will be

described in the manufacturer’s instructions. These will improve the cos-

metic appearance of the recorded images. Suffice it to say here, for expo-

sures of less than a second you will probably not need to subtract a dark

frame provided you have the cooling unit switched on. Whether you will

have to make a flat field exposure will depend upon the quality of the

CCD. Recourse to the manufacturer’s explanations and instructions,

together with the results of your own experimentation, will soon settle

this point.

I do realise that the set-up procedure I have given here is idealised. At

least for your first attempts the sequence may be rather more muddled. For

instance, you won’t be able to focus properly until the exposure is at least

approximately correct to start with. However, a little practise will soon

work wonders and will make setting up a streamlined and swift affair.

After making some further trial exposures of differing lengths in order

to get the best-looking image you can begin the serious process of imaging

the Moon. You could perhaps store the images as files (TIF or GIF format files

are normally preferred among amateur astronomers) on disk or in the com-

puter’s memory.

Maximising the resolutionIn the same way as for imaging onto photographic film, the image will nor-

mally have to be enlarged from that at the principal focus in order that the

limiting resolution of the CCD does not restrict the achieved resolution of

the image. The theory and practice of enlarging the primary image is

covered in Section 4.4.

The fact that the imaging area of the CCD is physically much smaller

than that of the normal photographic film frame will mean that it is much

less afflicted with outfield blurring if you decide to use eyepiece projection

as the method of primary-image amplification.

What enlargement factor do you need? Here the Nyquist theorem is a

useful guide. As it applies in our case it means that the smallest details

resolved in the image ought to be sampled with at least two CCD pixels. Less

than that and the image will be under-sampled and some of the resolution

will be lost. Also, spurious details may be generated by the undue promi-

nence of the ‘blocky’ nature of the CCD matrix. For imaging with a good-

quality telescope of up to about 12 inches (305 mm) in aperture one might

set the desired resolution as that imposed by the diffraction limit (dis-

cussed, with formulae, in Section 3.1).

By Rayleigh’s formula, a 12-inch aperture should resolve down to 0.45

arcsecond. Of course this is better than the seeing prevalent at most sites

will normally allow but it is better to ‘aim high’. However, it would be as

5.2 CCD ASTROCAMERAS IN PRACTICE 105

much of a mistake to aim too high. For a given CCD, the area of the Moon

imaged will also be at a premium. Filling the available picture area with a

very blurry view of a single small crater is hardly desirable!

If we were using a CCD with 15 �m (1.5�10�5 m, or 1.5�10�2 mm) sized

pixels, then we should arrange that the smallest details resolvable should

cover two adjacent pixels (a linear distance of 2�1.5�10�2 mm, which is

equal to 3�10�2 mm). As an example, let us say that we are using a 12-inch

telescope and hope to capture details at the diffraction limit. Hence the

image scale we need is 0.45/3�10�2, or 15 arcseconds/mm. To get that

image scale we need an effective focal length of 206265/15, or 13551 mm

(Equation (4.1), relating image scale to effective focal length, is given in

Section 4.2). This is an effective focal ratio of f/44.

It might be useful to realise that this ‘diffraction-limited – Nyquist

limit’ is attained for a 15 �m CCD in use with any optical system of this

effective focal ratio (because the image scale is proportional to the aperture

for a given focal ratio, and the resolving power is also proportional to the

aperture). The same limit is reached with an effective focal ratio of f/30

when using a CCD with 10 �m sized pixels, and f/60 (in round figures) for

one with 20 �m pixels.

Given normal seeing conditions, I would advise against further propor-

tional increases in focal length for apertures larger than 12 inches. Instead,

use the extra aperture of the telescope to deliver images to the CCD at a

lower effective f/number. The extra brightness will allow shorter exposures

to be given and so increase the chances of getting that elusive sharp image

amid the usual turbulence. At any rate, that is what I would do. I recom-

mend experimenting to find out what best suits your own equipment and

the conditions at your own observing site.

Once you have your images stored on disk or in the computer memory

you can take advantage of one of the major bonuses that comes with this

technology: enhancing them by the use of image-processing software.

More of this in Section 5.4.

5.3 VIDEOING THE MOON

Take a look at Figure 5.3. It shows the great crater Plato and part of the

Montes Alpes. I took this photograph using my own telescope, though not

by means of conventional film photography, nor by the use of a proper CCD

astrocamera. In fact, I used my own domestic video ‘palmcorder’.

The seeing was very ordinary that night and yet the resolution of the

image approaches the 1 arcsecond level. It is, you will have to take my word

for it, depressingly rare for the seeing to allow details any finer than that

to be seen (or even just glimpsed) from the garden of my home in Sussex,

England.


Using conventional photography, I would have had to take more than

one hundred exposures in order to have a fair chance of getting just one

that shows details as fine as this on the same night. Yet this picture is not

a fluke. Take a look at Figures 5.4, 5.5 and 5.6, also made in the same video-

ing session, showing other parts of the Moon that night.

The telescope I used was my 181⁄4-inch (0.46 m) reflector but the seeing

was the limiting factor in the resolution of the images, not the size of the

telescope. You could have done just as well as I have with a telescope of less

than half the aperture of mine. In better seeing conditions you could easily

improve on my results. In the following notes I explain how.

The video cameraIf you already own a video camera, then put that one into service with your

telescope. I am sure that you will be delighted with the results. However, if

you are wishing to buy one with the express purpose of using it with your

telescope (and all the other uses for it are a mere bonus) then I recommend

considering a few factors before making your choice.

5.3 VIDEOING THE MOON 107

Figure 5.3 Video image ofthe Moon taken by theauthor, using his 181⁄4-inch(0.46 m) reflecting tele-scope on the date and timeshown. The large crater atthe lower right is Platoand the mountain rangeextending from the upperleft to Plato is part of theMontes Alpes. Furtherdetails in text.

After its cost, one important consideration is the camera’s size and

weight. Though it is sometimes possible to successfully arrange the camera

on a separate tripod and have it peering into your telescope, you will nor-

mally have to have the camera riding on the telescope. I have achieved some

success in hand-holding the camera to the eyepiece but the results are

decidedly hit and miss, especially as holding the camera still for long

periods is difficult.

Even a ‘palmcorder’ type of camera will have a mass of about a kilo-

gram. You also will have to construct something to do the job of firmly

attaching the camera to the telescope. The heavier the camera is, the firmer

– and this usually means heavier – this contraption will have to be. Will

your telescope remain shake-free with all this weight hanging close to the

eyepiece? Do not forget that you will also need to add counter-weighting to

re-balance the tube and/or the mounting!

Consequently, unless you own a telescope which is constructed like a


Figure 5.4 The north polarregion of the Moon. Avideo image taken by theauthor at the date andtime shown. Furtherdetails in text.

battleship, I recommend selecting a video camera which is as lightweight

as possible.

The next thing to worry about is the resolution of the camera.

Obviously it should be as great as possible. All modern video cameras

have CCDs as their image detectors. A low/medium-quality camera will

have a ‘1⁄3-inch CCD image sensor’, more expensive models having a ‘1⁄2-

inch’ version. You will normally find the figures for picture resolution,

and size of CCD in the technical specifications section of the instruction

manual. I recommend that you insist the storekeeper opens the box so

that you can examine the manual prior to purchase. The stated picture

resolution is often that in the horizontal direction. The vertical resolu-

tion is usually slightly better. A ‘1⁄3-inch CCD’ camera ought to have a hor-

izontal resolution of more than 200 lines across the full width of the TV

frame.

Unlike the older video cameras which used vidicon tubes as their

sensors, all modern cameras are very light sensitive. On the low light level


Figure 5.5 Another videostill of the Moon obtainedby the author using histelescope, this time of theregion of the craterRegiomontanus (the largeformation just belowcentre, containing thevolcano-like structure onits floor). The date andtime the image was takenis displayed at the lowerleft.

exposure setting mine records in illumination levels as low as 1 lux. Using

my camera with my 0.46 m telescope, I was able to successfully record the

dust shells around the nucleus of comet Hale–Bopp. You should not have

any trouble in recording the Moon’s vistas through the camera, even when

using a telescope of quite small light-grasp. On the contrary, you might

even have to take precautions against too much light if you use a low mag-

nification on a large-aperture telescope!

There is one major pitfall I must warn against: do not purchase a video

camera which has no manual override for focusing. Using a video camera

on ‘automatic focus mode’ to try and image the Moon through the tele-

scope is doomed to failure. Do so and you will find the camera’s electron-

ics will not like the image your telescope delivers one little bit. The camera

focusing mechanism will restlessly zoom and jitter about the mean focus

setting. Trying to watch the playback will make you feel very queasy! You

must be able to focus the camera manually.

I purchased my video camera at the beginning of 1994. It is a National

Panasonic NV-S20B and cost me just under £600 (about $1000). It is a ‘palm-


Figure 5.6 Part of theMare Imbrium, the largestcrater being Archimedes,imaged by the author atthe date and time shown.Other details as for Figures5.3, 5.4 and 5.5.

corder’ having a mass of just under 1 kg without its batteries (it can be

powered by a transformer at the end of a long, lightweight, cable if

desired). The ‘1⁄3-inch CCD sensor’ has a horizontal resolution of “more than

230 lines”, according to the specifications. The camera has the facility for

on-screen recording of the date and time, if desired, as well as a selection

of ‘shutter speeds’ which allow one to optimise the image quality for dif-

ferent lighting conditions. More about the usefulness of this function later.

The camera lens can ‘zoom’ between effective focal lengths of 5 mm (the

widest-angled view in normal use) to 40 mm for close-ups. We need the lens

set to ‘maximum zoom’ (‘�8’, 40 mm effective focal length in the case of

my camera) when using it with the telescope.

Mounting and shootingI certainly do not recommend attempting to remove the lens of your video

camera. So, you are forced to leave the telescope eyepiece in place and use

the ‘infinity-to-infinity’ focusing method, as described in Section 4.4.

The camera needs to be mounted so that it looks squarely into the tele-

scope eyepiece. Figure 5.7 shows how I attach my video camera to my 0.46 m

telescope. There are as many solutions to the problem of mounting the

camera on the telescope, and ways of achieving the necessary re-balancing

of the telescope, as there are different telescopes. It is purely a matter of


Figure 5.7 The arrange-ment the author uses toattach his video camera tohis telescope.Counterweights (notshown) attach to thebottom end of the tele-scope tube to restore thebalance.

mechanics. Even if the publisher were to allow me many extra pages in this

book so that I could outline several of the possible solutions, the chances

are that I would still not cover anything that is suitable for your particular

telescope and camera, given the tools and materials you have at your dis-

posal. So, the mechanics of achieving the mounting of your camera onto

your telescope I must leave to you.

At least Figure 5.7 might provide some inspiration. Note how I have pro-

vided some adjustment for ‘squaring on’ the camera to the eyepiece – nec-

essary to get the best-quality images. I have also made some provision for

racking the camera back and forth, which is a great convenience when

using different eyepieces and for initially setting everything up – particu-

larly changing eyepieces and focusing, when some clearance will be

needed in front of the camera lens.

The Moon is in the sky and we have just set the camera into its mount-

ing, fitted to our telescope, and have also attached the counterweighting.

The telescope is balanced and ready to turn towards the Moon. We have

already made sure that the camera focus is set to ‘manual’ and that the

focus ring is moved all the way to ‘infinity’ (long distance) focus position,

also that the ‘zoom’ setting is to maximum (more about this shortly) and

that the camera is otherwise ready for operation.

With the camera set back as far as possible from the telescope, plug a

low-power eyepiece into the telescope drawtube. Adjust the rackmount so

that the eyepiece is close to its normal position for infinity focusing.

Perhaps a pre-determined felt-pen mark on the drawtube would be a useful

guide, since you will not be able to get your eye to the eyepiece with the

camera in position.

If the eyepiece is fairly close to its correct infinity focus position, then

the camera can be safely brought up so that its lens is a centimetre or

two from the eyepiece but do leave room enough for any necessary fine

adjustment.

Now it is time to point the telescope towards the Moon. My comments

here follow those already given in Section 5.2. At the point where the

moonlight is dropping into the telescope drawtube you will probably be

able to see it emerging from the eyepiece and illuminating the camera

lens.

Powering-up the camera and looking through its viewfinder, you ought

to be able to easily find the Moon’s image and set the telescope on the part

of it that you want to record. At this point you can make any fine adjust-

ment necessary to the telescope focuser but please do be very careful that

you do not drive the eyepiece into collision with the camera lens! If

desired, you can now bring the camera a little closer to the eyepiece,

though a gap of a centimetre or so will make no difference; the camera lens


is big enough to capture all the emergent rays without it having to be in

extremely close contact with the eyelens of the eyepiece.

Having brought the image to as fine a focus as possible, you should now

be seeing an impressive view of the Moon’s mountains and craters. Try the

various camera exposure settings. The shortest on my camera is the so-

called ‘sports’ setting. This produces the best result with my telescope. The

image is sharpest at this setting because the effects of turbulence and any

tremors of the telescope are virtually ‘frozen’ on individual frames.

Also, I find that my 0.46 m telescope gathers too much moonlight for

the camera to cope with on the other settings. On my first attempt, I found

that a black curtain effect (caused by severe overload) descended over the

image when the Moon entered the field on all but the ‘sports’ exposure

setting. Even if your telescope is rather smaller than mine, you will prob-

ably find that the fastest exposure setting will give the best recorded

image.

Of course, the magnification of the image, the transparency of the air,

etc., will all determine the correct exposure. At least you can see what is

happening through the viewfinder while you select the different exposure

settings on the camera – a big advantage over silver halide photography!

You might be satisfied with the view you already have through the

camera and can set it recording onto its own tape. Alternatively you might

wish to change the eyepiece to give a higher magnification. More on this

later, though here is the place to explain why the camera ought to be left

on a setting close to full zoom.

The reason is that on lower settings (at which the camera lens has a

shorter effective focal length) not all of the rays emerging from the eye-

piece can find their way unobstructed through the camera lens assembly.

If you experiment with the camera on the telescope you will find that on a

low zoom setting the image appears as a small island in a sea of surround-

ing blackness. Press the zoom button and you will find that this patch

expands in size. Nearly full zoom will be needed before the image fills

the field.

If you can successfully mount your video camera onto your telescope,

and get it balanced properly, you will find this technique very forgiving as

regards any other requirements of your telescope. An equatorial mount is

a great convenience, while a drive is very much a luxury. You could even

get superb results from an undriven altazimuthly mounted telescope.

There are other advantages in using a domestic video camera: the images

are in full colour and one can record a commentary at the same time as

recording the view through the telescope – though you might warn the

neighbours, lest they become perturbed on seeing you apparently chatting

to yourself while at your telescope!


Field of view and image scaleThe effective focal length and effective focal ratios are calculated in the

same way as for a conventional camera in the infinity-to-infinity configura-

tion (see Section 4.4). By way of an example, the photographs shown in

Figures 5.3, 5.4, 5.5 and 5.6 were all taken with my 0.46 m reflector, which

has a focal length of 2.59 m. My camera, with its lens adjusted to ‘full zoom’

(effective focal length 40 mm) was set looking into an 18 mm focal length

Orthoscopic eyepiece. The amplification factor was 40/18, or 2.22. Thus the

effective focal length of the combination was 5.76 m, and the effective focal

ratio was f/12.4.

Knowing the effective focal length, the image scale can be calculated.

In this case it was 206265/5760, or 35.8 arcseconds per millimetre.

However, I do not know the precise size of the CCD so this figure is only

useful in making a rough prediction of the area imaged. The “1⁄3-inch” size

of the CCD is only a rough guide. It is a category, rather than a precise

figure, and refers to the approximate (and usually exaggerated!) length of

the diagonal between corners of the CCD’s imaging area. If your video

camera has a ‘1⁄3-inch’ CCD you can expect it to have an imaging area of

something like 4.0 mm�5.3 mm.

The area covered in each of the photographs presented in Figures 5.3,

5.4, 5.5 and 5.6 is approximately 140 arcseconds�190 arcseconds. The repro-

ductions are virtually the full frames photographed from my TV screen.

Maximising the resolutionYou might not know the size of the pixels in your camera but you can still

ensure that you do not under-magnify the image and so limit the potential

resolution. The manufacturer’s specifications sheet will provide you with

a figure for the resolution in terms of the size of the full frame. My camera

has a resolution in the horizontal direction of “more than 230 lines”. With

the arrangement of my telescope, camera and eyepiece already described

the width of the full frame comes out as 190 arcseconds. Therefore the

potential resolution of the image is 190/230, or 0.8 arcseconds.

On most nights I find that I can only glimpse arcsecond-level details, so

this choice of amplification is about right. Increasing the magnification

would serve only to reduce the field of view and produce a blurrier image.

However, on nights of perfect seeing my telescope ought to resolve down to

about 0.3 arcsecond. I could match this by exchanging my 18 mm focal

length eyepiece for one of 6 mm focal length. The potential resolution

would then be 0.28 arcsecond and the size of the field of view would be 48

arcseconds�63 arcseconds. Unfortunately, the very few instances I have

experienced seeing anywhere near that good have all happened before I

acquired my video camera!


Playback!Videoing the Moon is surely the easiest way of getting high-quality images of

it if, like me, you have limited facilities and a poor observing site. With more

than two-dozen images recorded every second, you can search out the few

best ones in each session. Your friends will be wowed by the impressive views

of the Moon you will be able to show them on your television screen. More

importantly, since these images are ‘hard copy’ they have real scientific

value. The contentious field of TLP research is one where hard-copy evidence

of any suspected anomaly is highly desirable. Not only would the evidence be

more believable, but also having hard copy enables scientific measurements

to be obtained from the images. More about TLP research in Chapter 9.

The video images you can achieve should be much better, in terms of

limiting resolution even if not in total area of the Moon imaged to a high

quality, than anything you can achieve through old-fashioned silver halide

photography. In fact you can make them better still if you can send the

images to your computer!

Linking your video to your computerThere is a way of sending the output of your video recorder/camera to your

computer. Your computer must be fitted with a piece of circuitry (in com-

puter jargon a card) known as a frame-grabber. If you are up to the job you

could install this hardware (and then install the operating software) your-

self. If not, then you will have to have a computer specialist do the job for

you. I am quite well practised in electronics. However, I am very much a

novice when it comes to computers. All my previous books were written on

my old AmstradWord Processor! After it gave eleven years of faithful (if slug-

gish) service, I decided that it was about time I put it out to grass and get

something more modern. As well as my replacement machine performing

as a word processor to enable me to write this book and those in the future,

I looked forward to the various other clever things it should be able to do.

I ordered a bespoke computer in 1996 (the specifications of which I

determined after seeking the advice of knowledgeable friends) and had

the supplier fit a frame-grabber card in it. What I got was a Hauppauge

‘VideoMagic’ Motion-JPEG video-capture card fitted into my Pentium 133 com-

puter. The computer has a 1.6 Gigabyte hard-disk and 32 Megabytes of RAM.

If those specifications seem laughable to you, remember in 1996 those

values of speed and memory were quite respectable! At the time of writing

(1998) the same money (£2000, $3200 – including the Windows ’95 and

Hauppauge ‘VideoMagic’ software and a Hewlett PackardDeskjet 690C printer)

would easily buy a system with twice the memory and processing speed.

Those figures will undoubtedly have further increased by the time you are

reading these words.


In most respects I am very pleased with the performance of the

package, though I am disappointed in the performance of the frame-grabber

itself. The software for processing individual frames is fine and I have

achieved impressive results in manipulating images sent to me on disk by

other astronomers. The system can do many impressive things, including

sampling sequences of video and processing them with a variety of special

effects for re-editing back into one’s home-made movies, etc. However, I

find the quality of the initially ‘grabbed’ individual frames is a little

lacking compared to the same frame ‘frozen’ on my VCR and displayed on

my TV. I have spent some while checking that all the software and hard-

ware settings are correct. They are. It seems that in doing many clever

things, the system does the one thing I particularly want less well! Of

course I can still enhance and manipulate my own video images, though

the quality of the end result must suffer because of the lower quality of the

initial grabbed image.

One very successful and popular frame-grabber/digitiser is the ‘Snappy’,

manufactured by Play, Inc. It plugs into the computer’s external user port,

so obviating the necessity of internal installation. Ron Dantowitz, a practi-

tioner of video imaging who gets outstandingly good results, uses a

‘Snappy’ frame-grabber as part of his system, so it is obviously a good one!

Now that I have begun to acquire a little knowledge and experience in com-

puters and image processing I can be sure that when I upgrade I will do so

rather more effectively than I did on my first attempt.

Once the raw image is in your computer you can perform various oper-

ations on it. Image processing is the subject of Section 5.4.

Other video systemsThe problem of fixing a weighty and bulky video camera to your telescope

can be avoided if you elect to buy or, if skilled in constructional electron-

ics, make for yourself a video system in which the imaging unit contains

just the CCD and the minimum of supporting electronics. This part of the

system is attached by lightweight cable to the rest of the imaging and/or

recording device. If you are prepared to deal with suppliers other than the

high street stores, you can obtain a variety of suitable CCD imaging units.

For instance, the major electronics manufacturer Philips produced a mono-

chrome CCD camera module as long ago as 1988. Despite its impressive

specifications, including a resolution of 450 lines and a sensitivity of 0.02

lux, it retailed at only £400 (about $640).

You will find suitable cameras supplied by security equipment retailers,

the major electronics firms, and (usually at higher cost) suppliers of astro-

nomical equipment. In addition, many electronics firms will sell you kits

for constructing your own CCD camera equipment.


You might well feel overwhelmed and confused when you start receiv-

ing information packages and brochures from the suppliers you seek out

but if you focus on six main requirements for your system you should soon

be able to settle on the one that meets your needs. I would prioritise the six

factors, with the most important first, as follows: compatibility with stan-

dard video recording equipment, cost, resolution, the weight and bulk of

the unit that attaches to your telescope, and ease of operation. Happy

hunting!

David Brewer, in the USA, and Martin Mobberley, in the UK were among

the first of the amateur astronomers to use video techniques in their

observing. That was back in the 1980s. There are now many others. I got sur-

prisingly good images of the Moon, myself, using a borrowed old vidicon-

tubed camera in 1985. Cameras have got very much better and cheaper

since then.

Thomas Dobbins, in Ohio, USA, produces superb results with a camera

that cost him only $400 (obtained from Hong Kong) in the mid-1990s. He

has written an account of his work, ‘Recording the Moon and planets with

a video camera’, in the December 1996 Journal of the British Astronomical

Association (Vol. 106, No. 6) and I recommend seeking this out.

I have already mentioned Ron Dantowitz of Boston, USA. My jaw

dropped open when I saw the illustrations in his article, ‘Sharper images

through video’, in the August 1998 issue of Sky & Telescopemagazine. As well

as obtaining stunning images of the Moon and planets, Dantowitz even

manages to resolve Earth-orbiting satellites and the Space Shuttle Atlantis!

The details of his technique are too involved for me to include here, and so

I recommend adding his article to your reading list. However, the key com-

ponent of his video system is an off-the-shelf commercial monochrome

CCD camera. A version of it, called Astrovid 2000, especially modified for

astronomical use, is currently (1998) available from Adirondack Video

Astronomy, who can be contacted at: 35 Stephanie Lane, Queensbury, NY

12804.

5.4 IMAGE PROCESSING

Once the digitised image is in your computer you can perform a wide

variety of operations in it. As well as manipulating the brightness levels,

colour hue, and saturation, of the image, one can perform various

enhancement procedures.

It is possible to combine frames or semi-frames, to stitch frames

together in order to build up a large area image from smaller components,

to apply various filters to enhance small-scale features, etc. What you might

try will, of course, depend upon the time, energy, and resources you have

available. Suitable software packages abound. A software package which is

5.4 IMAGE PROCESSING 117

particularly popular with astro-imagers at the time of writing is Adobe

PhotoShop.

This area is large and still growing. As well as keeping a lookout for arti-

cles in contemporary astronomy magazines, I recommend you keep an eye

out for recent books. Those ‘recent-ish’ as I write these words include:

Choosing and Using a CCD Camera, by Richard Berry, Willmann–Bell 1992; The

Art and Science of CCD Astronomy, edited by David Ratledge, Springer–Verlag

1996; and A Practical Guide to CCD Astronomy, by Patrick Martinez and Alain

Klotz, Cambridge University Press 1997.

I offer here just a couple of examples of image processing in action.

Figure 5.8(a), (b) and (c) shows how Terry Platt has started with a raw image

of the Moon and processed it to show fine details. Figure 5.9(a)–(e) shows a

sequence where I have applied further image processing to one of Terry

Platt’s already very good images. The details are given in the accompany-

ing captions. As you will see from Figure 5.9, operating the software is a

matter of clicking on icons and dragging slider bars. Fortunately, full

instructions are always supplied. Study these well and be prepared for

many hours of experimentation if you hope to become a virtuoso of image

processing.

Terry Platt began experimenting with CCD imaging in the 1980s, build-

ing his own equipment. Since then he has gone on to produce the Starlight

Xpress range of CCD astrocameras which are now sold world-wide. Terry has

kindly let me include a number of his superb images in this book. You will

find examples in Chapter 8, Figures 8.4(b) and (c), 8.13(d), 8.17(f), 8.33(c),

8.44(e), 8.46(c), and 8.47(a). CCD images by another enthusiast, Gordon

Rogers, are to be found in Figures 8.11(b) and 8.14(e). Details are included

with them.

As well as inputting images into your computer direct from the CCD

camera system, or from the frame-grabber attached to your video camera,

you could also digitise your own photographic transparencies, negatives or

prints. Suitable scanners are now becoming more affordable. All the

enhancement procedures can be applied to these images just as well as to

those originating from CCDs. I recommend seeking out a couple of Sky &

Telescopemagazine articles: ‘Digitally enhance your astrophotos’ in the July

1997 issue and ‘Digital desktop darkroom’ in the July 1998 issue. Although

both articles concentrate on deep-sky subjects, much of the material is also

relevant to the lunar imager.

5.5 GETTING HARD COPY

The printers for home computers available for a given outlay are getting

better. Ones that produce print-outs of truly photographic quality are now

easily within the financial reach of many people. Alternatively, if you lack


one of these, or if you wish to get hard copy direct from your TV or com-

puter monitor – for instance you may want still photographs from your

Moon videos as displayed on your TV – then you can do this as well.

However, there is more to it than simply pointing your camera at your TV

and snapping away. It is relatively easy to get good results but you have to

go about the task in the right way.

5.5 GETTING HARD COPY 119

Figure 5.8(a)–(c) Stages inthe processing of one ofTerry Platt’s images of theMoon.(a) ‘Raw’ image obtainedby imaging the Moon atthe f/5 Newtonian focus ofan 8-inch (203 mm)reflector (stopped to3-inch, or 76 mm, off-axis)onto the CCD of a StarlightXpress SFX camera. (b) Result of a non-linearcontrast stretch in order toimprove the details in thedark terminator region.

(a)

(b)

After the obvious basics of setting the camera up on a tripod in front of

the TV/monitor and aligning and focusing on the image as carefully as pos-

sible through the viewfinder, the room should be made as dark as possible

to avoid reflections showing up in the glass screen.

The film in the camera ought to have a speed of around ISO100–125.

Using the camera’s exposure meter (or a separate one if needed) select the

appropriate f/number that corresponds to an exposure of 1⁄4 second. You will

still have to use a wide aperture, perhaps f/4, but that is not the main

reason for selecting that particular exposure length.

The necessity for the long exposures is due to the way the TV generates

the viewing picture on its screen. The picture is synthesised from a small

spot of varying brightness that scans over the screen building up a raster.

This spot starts at the top left of the screen, moving to the right. Then it

rapidly starts again at the left of the picture but just a little lower than

before. The process continues down the screen.

In 1/50 second after the process started (1/60 second for televisions in the

USA) the spot has built up a partial picture composed of a grid of horizon-

tal lines with gaps in-between. In the next 1/50 second (1/60 second for tele-

visions in the USA) the spot starts again near the top left of the screen and

fills in all the missing gaps. In this way the interleaved scanning process

creates the illusion of a complete and fairly flicker-free picture every 1/25

second for UK televisions and 1/30 second for those in the United States.

The human brain may be fooled but the camera is not if the exposure

is too short – either a partial picture or one with light and dark bands on


Figure 5.8 (cont.)(c) Final result, after theimage sharpness has beenimproved by using a ‘high-pass filter’.

(c)


Figure 5.9(a)–(e) Furthermanipulation on theauthor’s computer of oneof Terry Platt’s superlativeCCD images.(a) ‘Original’ image. (b) ‘Tone adjustment’histogram for the‘original’ image (havingfirst ‘zoomed-in’ on aselected area).

(a)

(b)


Figure 5.9 (cont.)(c) Effect of altering theparameters (by draggingthe slide-bar controls inthe window) in order toimprove the visibility ofthe shadow details withinthe crater. Note the changein the parameters and thenew histogram.(d) Calling up the appro-priate window in order tosharpen the image.

(c)

(d)

it would be the result. The snag arises from the way the camera’s shutter

interacts with the image of the moving spot. For my earliest experiments I

used an exposure of 1/8 second and this proved to be only just sufficient to

avoid significant bands of lighter and darker image appearing. These broad

bands are caused by un-synchronised incomplete fields. Figure 5.6 is one of

those early results and the banding is slightly in evidence. The extra field-

sweeps comprising an image recorded in 1⁄4 second are enough to blend out

the banding.

For photographing video stills, the freeze-frame on your VCR must work

well. If it doesn’t, try adjusting the tracking control. This will usually calm

a fluttering image.

In his Journal of the British Astronomical Association article, referred to

earlier, Thomas Dobbins advocates combining several exposures in order

to reduce the ‘grain’ that often blights still images. He simply leaves the

video playing and makes his photographic exposure at the time he judges

the image quality to be at its best. However, he does record the Moon from

a site where the seeing conditions are much superior to those I have to put

up with.

I seldom get even two consecutive good frames, let alone a whole

sequence of a dozen or more of them. My best results come from carefully

searching out those individual frames where at least the central area of the

image reveals the sharpest details. I then photograph just those. Obviously

this needs a VCR with a good pause and frame-by-frame advance facility.


Figure 5.9 (cont.)(e) The final result. (e)

Nowadays all but the cheapest (less than four head) models of VCR should

be up to the job.

If having your off-screen Moon photographs commercially processed, it

is probably advisable to include a brief note explaining what the content

of the film is, when handing it over. Of course, doing the processing and

printing yourself does allow you to be fully in control. For instance, if the

TV screen’s phosphors are unduly prominent you can try slightly defocus-

ing the image to soften their appearance. Provided you do not take the

defocusing too far you should be able to produce a more aesthetically pleas-

ing result without any significant loss of lunar detail.

5.6 SOME CCD EQUIPMENT SUPPLIERS

This list is intended merely to get you started in your search for suppliers

of CCD equipment. It is not complete and, in any case, may well be out of

date by the time you read these words. It covers only the main suppliers of

dedicated astronomical CCD systems. Neither I, nor the publishers, would

wish to endorse one manufacturer’s products over those of another, nor

can become involved in any disputes between you and any supplier. This

list is for information purposes only.

Celestron International, 2835 Columbia Street, Torrance, California

90503, USA (Available in the UK from David Hinds Ltd., Unit 34, The

Silk Mill, Brook Street, Tring, Herts., HP23 5EF).

True Technology Ltd, Woodpecker Cottage, Red Lane, Aldermaston,

Berks, RG7 4PA, England.

Meade Instruments Corporation, 6001 Oak Canyon, Irvine, California

92620, USA (Available in the UK from Broadhurst, Clarkson and

Fuller Ltd., Telescope House, 63 Farringdon Road, London, EC1M

3JB).

Micro Luminetics Inc., 3447 Greenfield Avenue, Los Angeles, California

90034, USA.

Santa Barbara Instruments Group, PO Box 50437, 1482 East Valley

Road, Suite #33, Santa Barbara, California 93150, USA.

SpectraSource Instruments, 31324 Via Colinas, #114, Westlake Village,

California 91362, USA.

FDE Ltd., Foxley Green Farm, Ascot Road, Holyport, Berkshire, SL6 3LA,

England.


The physical Moon

This book is intended to be a ‘hands-on’ primer for the practical astrono-

mer who wishes to observe the Moon. As such, giving even the briefest

outline of lunar science, let alone giving details of how this knowledge

was obtained, may seem to be a waste of precious space. On the other

hand, while it is true that the Moon’s stunning vistas can provide many

hours of entertainment of the ‘sight-seeing’ kind, I would argue that

observing the Moon is ultimately a sterile and pointless exercise unless

one is attempting to understand and know it better. If you accept that

premise then it follows that having some knowledge and understanding

of the Moon (including knowing what mysteries still remain to be solved)

will expand, and give some meaning and purpose to, your observations

of it.

In that spirit I offer this highly abridged account of the space-borne mis-

sions to the Moon and some of our modern ideas about the physical nature

and evolution of the Moon that arose because of them.

6.1 THE FIRST LUNAR SCOUTS

In 1903 Orville and Wilbur Wright made their first powered flights at Kitty

Hawk. Astonishingly, it was only 66 years later that Neil Armstrong and

Edwin ‘Buzz’ Aldrin stepped from their space-going vehicle onto the

Moon’s alien surface. The pace of progress at that time was breath-taking.

Indeed, it was only in 1957, a mere dozen years earlier, that Sputnik 1, the

Earth’s first man-made satellite, was launched into orbit, marking the true

beginning of the ‘Space Age’. The many elements of progress – such as in

launch-vehicle design, probes, satellites, telecommunications, and much,

much, more – all form part of a complex story. Here, though, there is room

only to mention some of the main highlights of the saga of the space-borne

exploration of our neighbouring world.

125

CHAPTER 6

The first Moon mission successes came with three Russian probes in

1959. Luna 1 (at the time the Luna probes were called Lunik) was the first to

achieve a flyby, passing less than 5000 km from the Moon and revealing

that it has no significant global magnetic field. Luna 2made further meas-

urements as it headed towards the Moon, eventually impacting with the

lunar surface in the Mare Imbrium. It was thus the first man-made object

to make physical contact with the Moon. Luna 3was much more ambitious.

As well as making a full range of scientific measurements, its trajectory

carried it about 4600 km beyond the Moon so that it could look back and

photograph the Moon’s rear side. The images it transmitted to us might

have been of poor quality by modern standards but the Earth-averted hemi-

sphere had never before been seen. We learned much from those first

blurry photographs.

The next few years brought forth a mixture of successes and failures.

The continuing Luna series of probes, and a Zond probe (Zond 3 in 1965,

another mission to photograph the Moon’s averted face while it was on its

way to Mars – two objectives for the price of one!) were joined by the

American Ranger series of probes. Ranger 7 was the first to photograph the

Moon at very close quarters. As it hurtled to destruction in the Mare

Nubium in July 1964 (this part of the mare being re-named Mare Cognitum,

‘The Known Sea’, in commemoration) it took and transmitted back to Earth

over four thousand photographs. Altogether, nine probes bit the lunar dust

(and seven others either missed the Moon or were not intended to hit the

surface) before Luna 9 became the first soft-lander in February 1966. It

touched down in the Oceanus Procellarum, near the great crater Grimaldi.

Luna 10 became the first lunar-orbiting satellite in April 1966 and in the

next ten years 38 further lunar satellites and soft-landers were sent to the

Moon by the Russian and American space agencies (including the manned

missions, described in the next section). Among them the American Orbiter

series of lunar satellites, in the late 1960s, were particularly valuable in

mapping much of the Moon to a finer resolution than was ever possible

from the Earth. Of course, the mapping also included areas that were

either poorly seen, or totally hidden on the lunar far-side (see Figures 6.1,

6.4 and 6.5; also Figures 8.7(c), 8.13(g), 8.17(e), 8.22(h), 8.28(b), 8.33(e), 8.37(e),

8.41(e), and 8.46(d) in Chapter 8).

The American Surveyor craft also produced particularly valuable results,

as they were in effect soft-landing laboratories, sending back photographs

from their landing sites, as well as testing the mechanical properties and

chemical composition of the lunar soil. Meanwhile the Russians continued

with their Luna probes. Luna 16, launched in 1970, was the first robot vehicle

to return a lunar soil sample to the Earth. Luna 17 (better known as Lunokhod

1) did even better, in that it was the first robot rover vehicle to explore the

126 THE PHYSICAL MOON

Figure 6.1 The Moonviewed from an angleimpossible from the Earth.This Orbiter IV view of theMare Orientalis, clearlyshows the multi-ring struc-ture of this vast impactbasin. The inner, basalt-lava-flooded, section has adiameter of about 320 kmwhile the outermost ringspans about 930 km. Thesouth pole of the Moonappears at the top of thisphotograph and part ofthe near-side feature of theOceanus Procellarumappears to the lower left.The small patch of darkmare material between theMare Orientalis and theOceanus Procellarum (butclosest to the OceanusProcellarum) is the basalt-flooded crater Grimaldi(see Section 8.20 inChapter 8). (Courtesy NASAand Professor E. A.Whitaker.)

6.1 THE FIRST LUNAR SCOUTS 127

surface of another world. It spent over 10 months exploring the Moon’s

surface, covering about 10.5 km of the Mare Imbrium in that time. Luna 20

was another mission to recover lunar soil, this time from the Apollonius

highlands, in 1972.

The next year saw another Russian roving vehicle, Lunokhod 2 (Luna 21),

put down in the Mare Serenitatis – but of course the main glory in the years

1969–72 belongs to the Americans. For it was in those years that science

fantasy became science fact – and men walked upon the surface of another

world.

6.2 MEN ON THE MOON

While the unmanned probes were doing their work, preparations were

underway to send men into space. Major Yuri Gagarin was the first man

sent above the Earth’s atmosphere in the Russian Vostok capsule on 12 April

1961. Gherman Titov was next but the Americans were not far behind.

Colonel John Glenn was launched into space on 20 February 1962 in

Friendship 7, one of the Mercury series of manned capsules. I really wish

there was space available here to describe the events of the next few years

because the tale is a truly thrilling one. Instead, I must be content merely

to relate that the Americans eventually overtook the Russians in what unof-

ficially became known as “The Space Race”.

The American Gemini missions gave way to the Apollo programme. The

hardware to enable men to get to the Moon was designed, built and tested

in stages. The Christmas of 1968 was memorable because the astronauts

Frank Borman, James Lovell and William Anders became the first people to

travel beyond the Earth’s realm as their Apollo 8 spacecraft went into orbit

around the Moon. Only two more Apollomissions were required to further

refine and rehearse everything. Apollo 11 would be the one to achieve the

great goal.

On 16 July 1969 the mighty Saturn 5 three-stage rocket launched from

Cape Kennedy (previously known as Cape Canaveral, the name being

changed back again after the Apollo missions) with the astronauts Neil

Armstrong, Edwin ‘Buzz’ Aldrin, and Michael Collins riding in the nose-

cone capsule of Apollo 11. Stages one and two were released to fall away from

the rocket when their fuel loads were expended and their work was done.

The third stage finally put the astronauts and payload into orbit. The

payload consisted of the Service Module, at the top of which was the nose-

cone capsule (Command Module), and the Lunar Excursion Module, or

LEM, which was stored inside the upper part of stage three.

Three hours after launch the Command–Service Module was separated

and turned and the nose-cone attached to the LEM. The LEM was then

pulled out of stage three of the rocket. The Service Module engine was then


firedand stage threeof the Saturn 5 rocketwas left behindas theCommand–

Service Module and LEM together moved out of Earth’s orbit and headed

towards the Moon.

On 19 July the spacecraft was driven into lunar orbit. Armstrong and

Aldrin in the spidery-looking LEM (which had been named ‘Eagle’) separ-

ated from the Command Module, which was to stay in lunar orbit with

Collins keeping a lonely, if busy, vigil. Armstrong and Aldrin prepared for

landing. On Sunday 20 July the astronauts fired the LEM engine, slowing it

and allowing it to drop out of Lunar orbit and descend to its target on the

Moon – a site on the Mare Tranquillitatis. TV viewers watched the drama

unfolding. The world held its breath until Armstrong’s words: “Houston –

Tranquillity Base here – the Eagle has landed” were received with relief and

jubilation.

The astronauts peered through the spacecraft windows at the

unearthly scenery. They could see the long shadow of the LEM cast onto the

Moon’s dusty surface. Seven hours later Armstrong opened the hatch and

carefully climbed down the ladder. With the words “That’s one small step

for a man – one giant leap for mankind” (at least that is the official

wording. I have listened to the recording many times and I always hear “. . .

step for man”, missing the “a”, but I suppose I must be wrong) Neil

Armstrong became the first human to set foot on another world.

A little later Aldrin also stepped out onto the moonscape. For about 21⁄2

hours they busied themselves setting up a TV camera, planting the

American flag, taking photographs, collecting rock samples, and setting up

experiments on the Moon’s surface. Here on Earth millions of people

watched the astronauts go about their business and listened to the conver-

sations between themselves and Mission Control at Houston. The astro-

nauts moved with a bouncing, almost slow-motion, gait in the low surface

gravity (on the surface of the Moon objects have only one-sixth of their

earthly weight). All too soon it was time to climb back into the LEM.

After a night’s sleep the astronauts blasted off, leaving the lower part

of the LEM still sitting on the surface of the Moon, and re-joined the

Command Module. Then the journey home. On 24 July the Apollo 11 capsule

(just the nose-cone section) ploughed into the Earth’s atmosphere. Hung

under three large parachutes for the last part of its descent, the capsule

splashed down into the Pacific Ocean. The first great adventure was over.

Men had been sent to land on the Moon and returned safely to Mother

Earth.

Subsequent Apollomissions followed the same basic mode of transport-

ing men to the Moon (Saturn 5 launch vehicle plus payload, including LEM)

but with longer and longer periods spent on the Moon’s surface and pro-

gressively greater quantities of Moon rock and scientific data collected.

6.2 MEN ON THE MOON 129

Also, instrument packages were left to monitor conditions (temperatures,

seismic activity, solar wind data, etc.) and radio the information back to

Earth long after the astronauts had left.

The Apollo 12 astronauts Charles Conrad and Alan Bean landed their

LEM, ‘Intrepid’, in the Moon’s Oceanus Procellarum on 19 November 1969,

while Richard Gordon orbited the Moon in the Command Module. They

had landed only a couple of hundred metres from the Surveyor 3 probe

which had been landed there 21⁄2 years before. As well as carrying out their

other activities, they photographed the vehicle (see Figure 6.2) and added

a few parts of it to the booty they brought back to the Earth.

Apollo 13 nearly ended in tragedy as an explosion onboard the Service

Module put an end to the mission. The only option for the astronauts James

Lovell, John Swigert and Fred Haise was to carry on to orbit the Moon and

hope that the Service Module motor could be fired to get them back to the

Earth. They made it back despite the crippled state of their spaceship – a

sound reminder of the dangers of the enterprise (there had been previous

fatalities in both the American and Russian programmes).


Figure 6.2 ClearlySurveyor 3 bounced beforeit came to rest on thelunar surface, as revealedby this photograph of oneof its feet taken by anApollo 12 astronaut.(Courtesy NASA.)

Apollo 14 put the programme back on track. The LEM carried Alan

Shepard and Edgar Mitchell down to the Fra Mauro region of the lunar

surface (the first manned landing in rougher terrain) on 31 January 1971.

They hauled a small hand-cart about in two traverses of the lunar surface

while Stuart Roosa orbited in the Command Module.

The Apollo 15 LEM was landed at the foothills of the Lunar Apennine

(Montes Apenninus) mountain range on 30 July 1971. David Scott and

James Irwin drove over the lunar surface in their ‘rover’ vehicle (see Figure

6.3), covering 27 km in three separate traverses, including driving to the

edge of the valley Hadley Rille. Alfred Worden orbited in the Command

Module.

6.2 MEN ON THE MOON 131

Figure 6.3 Apollo 15 astro-naut James Irwin picturedby the Lunar RovingVehicle, with MountHadley providing aspectacular backdrop.(Courtesy NASA.)

Apollo 16 touched down in the Descartes region of the southern high-

lands of the Moon on 21 April 1972, with astronauts John Young and

Charles Duke in the LEM and Thomas Mattingly in the Command Module.

They also had a rover vehicle to aid in their exploration, experimentation,

and sample-collecting activities in the stunning rock- and boulder-strewn

environment. They also used equipment to make the first astronomical

observations from the Moon – ultraviolet photographs of the Earth’s

atmosphere, interplanetary gas and stars being particularly important.

Apollo 17 was the grand finale as the LEM, with Eugene Cernan and

geologist Harrison Schmidt aboard, touched down in the Taurus–Littrow

region on 11 December 1972. They went even further in their rover vehicle

(see Frontispiece). Each mission bettered the last with the astronauts

spending longer periods outside their LEM, doing more photography, and

making increasingly sophisticated geological examinations and scientific

experiments; also setting up more intricate remote telemetry packages.

As a result of the space probes, and particularly the Apollo programme,

our knowledge of the Moon grew a hundred-fold. When Cernan and

Schmidt rejoined Ronald Evans in the Command Module and they

headed back to Earth they brought to a close a period unprecedented in

human history.

6.3 THE POST-APOLLO MOON

Originally, the Apollo missions were to go beyond number 17 but the

public grew bored, and some vociferously objected to the money spent on

the project. Vote-conscious politicians cut back NASA’s budget. The pro-

gramme came to a premature end. Three successful Russian probes, and

one failure, went to the Moon post-Apollo, the last of these in 1976. To date

there have been no further manned missions.

We had to wait two decades before the next probe – Clementine – which

was injected into a polar lunar orbit in February 1994. By circling from pole

to pole as the Moon turned under it, the probe was able to photograph the

entire Moon in twelve different wavebands spanning ultraviolet through

to infrared (see Figure 8.41(e) in Chapter 8). Some of the images it obtained

were of particularly high resolution (the best showing details as fine as

100 m across).

It also carried a laser-ranging system which built up a laser echo map of

the Moon with a horizontal resolution of the order of 200 km, though with

a vertical sensitivity of about 40 m. The advantage of the laser echo tech-

nique was that the picture of the Moon it built up is three-dimensional, con-

taining as it does height information. For the first time scientists realised the

true extent of a depression in the Moon’s south polar region, known as the

South Pole–Aitken Basin. It turns out to be about 12 km deep and 2500 km


across, and holds the record for being the largest impact basin known in the

Solar System. Other ancient basins were also studied.

The multi-waveband images provide valuable information about

surface composition. Clementine was a multi-purpose probe, having mili-

tary as well as scientific goals. For two months it did its work orbiting the

Moon. It was then to be dispatched to a rendezvous with the asteroid

Geographos but a technical hitch caused it to be sent spinning off into

space, instead. As in the words of the ballad, Clementine was “lost and gone

forever”. Allied to the previous space-mission results, Clementine provided

another leap in our knowledge of the Moon.

More recently, (January 1998), the Lunar Prospector probe arrived at the

Moon (I will pass over the details of other probes which have passed by the

Moon on their way to other targets, even though some telemetry and

photography was undertaken). Like Clementine, it was sent into polar orbit,

following up on the investigations undertaken by the earlier probe.

Mapping, studies of surface composition, including the search for ice

deposits at the lunar poles, magnetometry, radioactive-particle counts and

gravitational data all were planned.

At the time I write these words the first results are coming in. NASA sci-

entists have announced the discovery of ice in the Moon’s polar regions;

about 6 billion tons of the stuff! This is probably all due to accumulated

materials from impacting comets and seems to be mixed up in the upper

regolith. However, I should caution that at the time of writing this finding

is not universally accepted. What the probe really detected was the signa-

ture of hydrogen in chemical combination – this may be water ice. The

mission is intended to last to the end of the year 2001 at the very least. We

can expect another big leap in our knowledge of the Moon by the time

Lunar Prospector has done its job.

6.4 NOT GREEN CHEESE BUT . . .The Russian Luna 16, Luna 20, and Luna 24 craft returned a total of about

0.3 kg of Moon rock. We already have about 41⁄2 kg of identified lunar

material on the Earth, in the form of meteorites blasted from the Moon’s

surface by impacting meteors, but it was the six Apollo manned landings

that provided us with the greatest quantity and variety of samples; some

381.7 kg in all.

The chemical composition of the Moon’s surface covering is very differ-

ent to that of the Earth. It is made up of a variety of igneous rock types. In

the main these are complex silicates. Unlike earthly rocks, there is a com-

plete absence of water in the chemical make-up of any of the samples so far

examined. As far as we can ascertain there is no water natural to the Moon

itself. Apart from anything deposited on its surface by external means, the

6.4 NOT GREEN CHEESE BUT . . . 133

Moon is a completely arid world. Nor did we find any signs of life, past or

present. In fact, the Moon has only trace amounts of the carbon com-

pounds that are needed as building blocks for the genesis of life as we know

it. Most of these compounds originated from outside the Moon (delivered

onto the Moon by the solar wind plus meteorite and comet impacts with

the lunar surface).

However, there are some similarities between the lunar rocks and the

exposed mantle materials we find on Earth (these are rare but occasion-

ally found amongst volcanic ejecta). Even more significant is that the

ratios of the proportions of the three common isotopes of oxygen we find

in the Moon-rock samples match closely with those we find in terrestrial

rocks.

The highland rocks and mare rocks are themselves very different from

each other. Considering the lighter-coloured highland material, there are

at least three major categories of distinct subtypes of the silicate-type

rocks. Ferroan anorthosites are particularly rich in calcium and aluminium

and largely composed of a mineral known as plagioclase feldspar. The so-

called magnesium-rich rocks are also plagioclase-based but also have mixed

in with them various magnesium-rich minerals such as olivine and pyrox-

ene. The minerals norite, dunite, and troctolite, are found in highland samples

but these are really subtypes of the magnesium-rich rock types, each

having various proportions of pyroxene, plagioclase and olivine.

The other major class of rock found in the lunar highlands is the so-

called KREEP. This is an acronym for potassium (chemical symbol K), rare-

earth elements (REE) and phosphorus (chemical symbol P). Rocks with

enhanced concentrations of these components are known as KREEP rocks –

an example being KREEP norite.

The lunar maria are composed of iron- and titanium-rich volcanic rock

types known as basalts. They also have a diversity of compositions within

the main type – pyroxenes, plagioclase and ilmenite (iron–titanium oxide),

olivine, plus many others. The lunar basalts have one important physical

characteristic. When they are heated to melting point their viscosity

becomes very low, much less than is the case for earthly volcanic lavas. To

give you some idea, the lunar lavas might have been as runny as the sump

oil in a cold automobile’s engine. This fact has an important bearing on

how the Moon got to look as it does to us today.

6.5 GENESIS OF THE MOON

Four main theories of the Moon’s origins were developed by theorists over

the years. The first of these is that the Moon was once part of the Earth but

broke away from it, leaving a hollow which became the Pacific Basin. We

now realise this idea is dynamically untenable. Also, the Moon’s chemical


composition is so unlike the Earth’s any simple separation would be out of

the question. This idea is now only of historical interest.

The second theory is that the Moon and Earth were formed at about the

same time, 4600 million years ago, but the two bodies were formed in com-

pletely different parts of the Solar System (which was also being ‘born’ at

the same time). At some later date, the theory goes, the paths of the Moon

and the Earth crossed and the Moon became gravitationally captured by

the Earth. Tidal interaction then caused the Moon to settle into a stable

orbit around the Earth. This idea is not totally out of the question but the

dynamical difficulties are very great and most theorists of today have little

confidence it. Further evidence against this idea comes from the oxygen

isotope ratios we measure in the lunar rock samples. These vary with loca-

tion in the Solar System but, as already noted, the ratio is the same as that

which we find for terrestrial rocks.

The mathematical difficulties associated with this second theory disap-

pear if we assume that the Moon and Earth formed in the same region of

space and at about the same time – the third theory. The isotope abun-

dance ratios would then also be explained. However, even allowing for the

chemical differentiation (heavier elements sinking to the core, leaving the

lighter elements on the top) that would take place inside a condensing

cloud of protoplanetary matter, it is very difficult to explain the sharp dif-

ference in the chemistries of the two worlds.

The fourth, and currently the most popular, theory we have today is

that at some time very early in the history of the Solar System, perhaps

before the Earth had developed a solid crust, our planet had a glancing col-

lision with another planet or protoplanetary body (perhaps it was even as

large as the planet Mars is today). This would have ‘chipped off’ a sizeable

chunk of material from both bodies. While much of the resulting shoal of

material and the remains of the second planet/protoplanet would be lost,

some of this debris would settle into orbit around the Earth and eventually

form a new body – our Moon. If the Moon was mostly formed from the

material that originated in the impacting protoplanet and from the

mantle of the Earth then this might explain the compositional differences

between the Earth’s and the Moon’s surfaces.

6.6 THE MOON’S STRUCTURE

The seismic detectors left on the Moon as part of the Apollo missions gave

us data for years after the last men walked on the Moon. Just as seismolo-

gists have built up a picture of the Earth’s structure by studying earth-

quakes, so planetary scientists have been able to build up a picture of the

Moon’s structure from the results of the very gentle moonquakes that

trouble the Moon’s globe. About 3000 of these were detected each year the

6.6 THE MOON’S STRUCTURE 135

seismic detectors were in operation. Lest you should get the wrong idea,

though, I should add that the total seismic energy output of the Moon is

less than one-ten-billionth the energy the Earth expends in earthquakes in

the same period – feeble by any standards. Moonquakes seem to originate

about 600–800 km below the lunar surface.

Also, a few spacecraft were deliberately smashed into the Moon’s

surface to generate much more violent tremors (and some moonquakes

have been triggered naturally because of meteorite impacts) to provide

further information about the Moon’s structure. In addition, the Apollo

astronauts also conducted seismic sounding experiments. Meanwhile the

various heat-flow experiments left by the Apollo astronauts indicate a heat-

energy flux of about one-third that of the Earth. Models suggest that most

of this heat energy is accounted for by radioactive decay deep in the Moon

and so the Moon must have lost most of the heat generated by its forma-

tion. These results have helped in the refining of the theoretical models.

The crust of the Moon extends to about 60 km depth and exists as three

distinct layers. The top layer is known as the upper regolith and is made of

fragmented and impact-welded rocks of the type geologists call breccias.

Ranging from 1 to 20 metres deep on average, the upper regolith is the

result of aeons of bombardment by meteorites large, small and minute

(micrometeorites), together with the crumbling stresses caused by the

diurnal heating and cooling. It could only form as it has on a world which

for a long time has been devoid of a protective atmosphere. The soil is also

churned and intermixed with materials from underlying layers due to the

same forces. This process has the delightful name of gardening.

Extending down to a depth of about 20 km is the lower regolith, com-

posed mainly of basaltic rocks. The bottom layer of the crust is chiefly made

up of the rock type known to geologists as anorthositic gabbro.

Below the crust is the mantle, rich in certain minerals such as olivine

and pyroxene. The mantle becomes less rigid with depth. Gravity data,

especially that obtained from the Lunar Prospector space probe, indicates the

presence of a small iron-rich core. It might be about 600 km across if com-

posed mostly of pure iron, increasing to about 1000 km if it is composed

mostly of iron sulphide. It cannot be larger than that because the density

of the Moon averages a mere 3.34 times that of water, too low to support a

larger core. Overall, the Moon’s globe is very iron-depleted compared to the

Earth. Given that the Moon has no significant global magnetic field

(though there are concentrations of weak magnetism ‘frozen’ into the

surface rocks), it is reasonable to suppose that the core has now solidified.

The presence of an iron-rich core is significant in that the most popular

theory of the creation of the Moon (see the previous section) should

produce a completely iron-free Moon if the impact had occurred after the


two colliding planets/protoplanets had become chemically differentiated.

Assuming the theory is correct, perhaps either or both were still so ‘new-

born’ as to be largely undifferentiated when the collision occurred?

I mentioned that the lunar crust is about 60 km thick. Actually, this is

only an average figure. It is much thinner on the Earth-facing hemisphere,

being only 20 km or so in places. However, on the reverse side the crust is

over 100 km thick.

The Luna 3 probe of 1959 had revealed there to be an almost complete

absence of maria on the Moon’s reverse side, yet about one-half of the

Earth-facing hemisphere is mare-covered. This was a real surprise to scien-

tists at the time. The reverse side of the Moon is covered with the same sort

of rough, cratered terrain we see in the highland areas of the near side. We

now understand the reasons for the asymmetry. The explanation is bound

up with the evolution of the Moon after its formation, so let us briefly

review our modern ideas on this subject.

6.7 THE EVOLUTION OF THE MOON – A BRIEF OVERVIEW

When the Moon was still a molten body, about 4600 million years ago, its

own gravity operated on the components making it up and caused the

heaviest to sink towards the core – the chemical differentiation already

referred to. The separation continued until the lightest elements floated

to the top. These lightest materials formed the basis of the lunar high-

lands. At the time when the Solar System was still young, space was clut-

tered with debris left over from the formation of the various planets and

moons.

During these early times massive lumps of material were smashing into

the Moon and the other planets. Great basins and smaller craters were

created by these massive, explosive, impacts on the now solidified lunar

surface. The gravitational fields of the Moon and the planets acted as ‘celes-

tial vacuum cleaners’, gradually disposing of the Solar System leftovers. All

the biggest pieces were used up first, only the progressively smaller pieces

of debris being left as time went on.

The ferocity of the lunar Blitzkrieg abated until it was all but over by

about 3800 million years ago. The Moon’s surface was then heavily scarred

and saturated with craters of all sizes, though with the greatest numbers

of them being the small ones.

I ought to mention that for many years a great controversy raged

among astronomers concerning the origin of the Moon’s craters. Setting

aside those with really wacky ideas, of which there were many, astrono-

mers dichotomised into two camps. Many maintained that the craters were

formed by endogenic (internal) processes. Endogenicist’s theories ranged

from violent volcanism, through to more quiescent mud-bubble scenarios.

6.7 THE EVOLUTION OF THE MOON – A BRIEF OVERVIEW 137

The evidence they drew on to support their views included a perceived non-

random distribution of craters on the Moon (north–south going crater

chains), and the fact that smaller craters almost always break into larger

ones – and virtually never the other way round.

In fact, the primary craters of the Moon are pretty well randomly

arranged. Much of the perceived north–south alignment is due to the

direction of the incident sunlight, which throws features along the lunar

meridians into prominence. This is particularly so when the terminator

looms close. In my view, the extreme rarity of larger craters breaking into

smaller ones is a little more convincing but even this factor is explainable

under the exogenic theory, otherwise known as the impact theory – the idea

that the craters were created by meteorites impacting with the lunar

surface.

I am sure that some readers will think I have displayed an unacceptable

bias in disposing of the endogenic theories so tersely, without even going

into a proper account of them. I wish I could say more here but I must

reserve such space as I have for the scenario that most scientists now accept

as correct. As an attempt to redress the balance can I please refer interested

readers to The Craters of the Moon by Patrick Moore and Peter Cattermole.

Published by Lutterworth Press in 1967, this is the last book-length account

of the endogenic theory that I am aware of, although Patrick Moore does

devote some space to it in his 1976 book Guide to the Moon, also published

by Lutterworth Press. Though both these books are long out of print,

perhaps you might pick up second-hand copies, or the inter-library loan

service might obtain them for you?

I cannot resist showing you the crater pictured in the centre of Figure

6.4. There can be no controversy about the origin of this one – it was created

by the impact of the spacecraft Ranger 8!

At an early stage after formation of the Moon, tidal drag between the

Earth and Moon locked it into a synchronous orbit with the Earth. Hence

it always keeps the same face to the Earth. Moreover, their mutual gravity

produced some asymmetry in the internal structure of the Moon, for

instance it bulging towards the Earth a little and having the thinnest part

of its crust on the Earth-facing hemisphere.

The creations of the biggest basins were real Moon-rocking events,

leaving a heavily fractured crust, some of the fissures extending down to

the still-molten mantle. Low-viscosity lavas flooded out of the fissures to fill

the basins and so form the maria.

Where the crust was thickest the fissures could not reach through to

the mantle and the basaltic lavas could not escape to flood the surface.

That is why the maria are predominantly on the Earth-facing hemisphere.

The crust was too thick to allow the process to happen on the reverse side.


As the interior of the Moon cooled, so the lava-flooding activity dwin-

dled and eventually stopped about 3200 million years ago. Some small-

scale volcanism probably continued for a little longer and the Moon

certainly continued to receive impacts thereafter but all the really major

activity was over and the Moon then became a much more sedate place.

6.8 LUNAR CHRONOLOGY

The 4.6 billion year history of the Moon has been divided into a number of

periods, or eras, marked by specific events. These have been dated by means

of the laboratory testing of soil and rock samples brought to Earth. Various

techniques have been used to date other lunar features/events with these

as primary benchmarks.

The first of these events was the formation of the Nectaris Basin – which

later lava-flooded to form the Mare Nectaris (the subject of Section 8.30 in

Chapter 8). This occurred some 3.92 billion years ago, according to modern

determinations. The first lunar era is thus the Pre-Nectarian Period (4.6 to

3.92 billion years ago). The massive amount of bombardment the Moon suf-

fered at this stage has obliterated much of the earliest formed surface

features, though an undefined number of Pre-Nectarian structures have

survived.

6.8 LUNAR CHRONOLOGY 139

Figure 6.4 A man-madelunar crater! The 131⁄2 kmdiameter crater at thecentre of this Orbiter IVphotograph was created bythe impact of the spaceprobe Ranger 8. It even hasa central peak! (CourtesyNASA and Professor E. A.Whitaker.)

The second benchmark event is the formation of the Imbrium Basin

some 3.85 billion years ago. This basin was later lava-flooded to form the

Mare Imbrium – the subject of Section 8.24 in Chapter 8.

The period between the formation of the Nectaris and Imbrium basins

(3.92 to 3.85 billion years ago) is known as the Nectarian Period. Here the

determinations of the ages of lunar formations become much more clear-

cut. The Moon was still suffering a very heavy bombardment but this had

reduced enough so that most of the basins, craters, and other formations

created at this time were not completely obliterated by subsequent

impacts. About a dozen of the basins we recognise today were created by

gigantic impacts in the Nectarian Period, along with thousands of craters.

The lunar soil was heavily churned and mixed by the pounding it received

during this time.

The ‘carpet-bombing’ continued to abate during the Nectarian period.

After the Imbrium impactor had done its work, only the projectile that

created the Orientalis Basin (see Figures 6.1 and 6.5) a few hundred million

years later remained as the last really massive piece of debris to hit the

Moon. Smaller fragments, though, continued to rain down.

The next accurately-dated event was the formation of the crater

Eratosthenes, some 3.2 billion years ago. This crater is described, and pic-

tured, in Section 8.5 of Chapter 8. The period between the formation of

the Imbrium Basin and Eratosthenes defines the Imbrium Period. Materials

ejected from the enormous explosion site of the Imbrium Basin are scat-

tered over a substantial portion of the Moon’s globe and the shock waves

that permeated the Moon caused much restructuring of the lunar topog-

raphy. I discuss some of the physical evidence that remains of this Moon-

shaking event in Chapter 8. It is during the Imbrium Period that most of

the basaltic lava-flooding of the basins occurred.

The formation of the crater Copernicus (see Chapter 8, Section 8.13),

0.81 billion years ago, provides the last of the key chronological markers.

The Eratosthenian Period (3.20 to 0.81 billion years ago) betwixt the forma-

tions of Eratosthenes and Copernicus saw the last vestiges of the episodic

lava-flooding of the maria and the continuing diminution of the meteor-

itic bombardment of the Moon.

This brings us to the Copernican Period, which spans 0.81 billion years

ago to the present day. Very few of the large lunar craters are younger than

Copernicus and only the most minor volcanic happenings have disturbed

the Moon’s quietude in the last billion years.

6.9 FILLING IN THE DETAILS

In order to economise on space, I have had to paint the account of our

modern ideas with an extremely broad brush. Consequently, I may well be


Figure 6.5 The north-eastern sector of the MareOrientalis. This is anenlargement of the viewshown in Figure 6.1. Theoutermost rings are justvisible on the limb of theMoon as seen from Earth(as a series of mountainranges – the basin beingvirtually edge-on to us),when the libration andlighting angles are mostfavourable. In fact, H. P.Wilkins and Patrick Mooredrew attention to the pos-sibility of there being a far-side lunar sea in the 1940s.They named it MareOrientalis, meaning the‘Eastern Sea’ because it layon the side of the Moon wethen called the east. Ofcourse, by the IAU conven-tion this is now the lunarwest!The impactor that

created the basin, the lastreally big chunk of debristo hit the Moon, was prob-ably a piece of rocky debrisseveral tens of metresacross. The concentricrings are, in effect, ‘frozen’shock waves in the lunarcrust. Radial features arealso apparent, especially inthe outer parts of thestructure, including sec-ondary impact scars.(Courtesy NASA andProfessor E. A. Whitaker.)

6.9 FILL ING IN THE DETAILS 141

guilty of giving the impression that lunar science is simple and straightfor-

ward and, even worse, that we now know all there is to know. Nothing

could be further from the truth.

For instance, the way space probes behaved in lunar orbit led to the

early discovery that there are distinct concentrations of dense material sit-

uated some way beneath the lunar surface. These are known as mascons, a

contraction of ‘mass-concentrations’. The first results suggested that these

all coincided with the lunar maria. It was assumed that the lunar maria

were made of denser-than-average materials, which they are (being mantle

material brought to the surface), and this explained the anomalies. In

recent years the picture has grown more complicated. In particular, Lunar

Prospector found several new ones, including four on the lunar far-side, but

only some of these coincide with lunar maria. The latest thinking is that

the mascons result from dense plumes of convected material from deep in

the Moon, rising into its upper mantle. If that is right, I wonder if the basin-

forming events somehow triggered lunar mantle plumes to preferentially

form under the fractured basin floors, given that most mascons are asso-

ciated with the maria?

My speculations aside, it is only relatively recently that geologists have

appreciated just how important mantle plumes are in explaining earthly

tectonic and volcanic structures and activity. A salutary lesson that we still

have much to learn!

The entire spectrum of lunar features and all the myriad pieces of evi-

dence – those obtained from remote viewing the Moon as well as actual

samples of lunar material – have had to be woven into a coherent scenario.

The overall scheme might appear simple but the details are rather

complex. Given that the main purpose of this book is to be an observer’s

guide, I have incorporated many of our modern ideas into the accounts of

selected lunar features I provide in Chapter 8.

What is the nature of the brilliant ray-systems that some craters

possess and why do not all craters have ray-systems? Why do some craters

have much brighter interiors than others? What causes the wrinkle

ridges on the lunar maria? What are the nature of the lunar rilles and

how did they come about? You will find answers to these questions, and

more, in Chapter 8. However, for a much more complete account of our

post-Apollo ideas about the physical nature and evolution of the Moon I

can recommend two books, both published by Cambridge University

Press. The Moon – Our Sister Planet, was written by Peter Cadogan and pub-

lished in 1981. Larger, and more up to date (published 1991) is Lunar

Sourcebook – a User’s Guide to the Moon. Together, these give a very compre-

hensive overview of our understanding of the Moon as it stood at the end

of the 1980s.


What about more up-to-date information, such as the knowledge we

have learned from Clementine and Lunar Prospector? The next chapter, which

in part serves as resource guide, will help you locate a selection of materi-

als available at the time of writing (1998), as well as incorporating a key

map which you will find useful in finding your way to the selected lunar

features examined in Chapter 8.

6.9 FILL ING IN THE DETAILS 143

The desktop Moon

This very short chapter deals with matters of interest to the amateur

working at the desk and computer. In most cases this desktop work will be

supplementary to the activity carried out at the telescope. A few people

might conduct all their lunar exploration from their desk and computer

and I hope that the notes given here will be of some use to them, also.

However, this book is intended for the telescopist and since I can only pack

so much into the space set by the publisher I must be honest and say that

others will probably find this treatment inadequate.

So far I have suggested various books and articles that you might find

of use in connection with the subjects covered in each of the foregoing

chapters. This chapter is partly a resource guide, in which I ‘mop up’ some

references and materials not mentioned elsewhere. Aside from that, I have

included details of the methods for obtaining the heights of lunar features,

as many will find this an interesting exercise. After a survey of the lunar

maps and atlases available, I finish with an outline chart that I have pre-

pared as a key map for locating the lunar surface features explored in the

next chapter.

7.1 THE LUNAR SOURCEBOOK

Yes, I have mentioned this earlier but it deserves my highest recommenda-

tion. If you want a large (over 700 page) single-volume guide to the science

of the Moon then you can do no better than to invest in a copy of the Lunar

Sourcebook – a User’s Guide to the Moon. It is edited by G. Heiken, D. Vaniman

and B. French and was published by Cambridge University Press in 1991.

It is chock-full of data, information and explanations about the physics,

chemistry, and geology of the Moon and how that information was

obtained. It includes a list of hundreds of references to scientific papers

and the details and contact addresses of many sources of lunar databases,

145

CHAPTER 7

imagery and archives. It is a superb springboard to further studies as well

as being a mine of information itself!.

7.2 SPACECRAFT IMAGERY

The amateur astronomer is not limited to the views of the Moon he/she gets

through his/her telescope. Spacecraft imagery is now available in various

media.

BAA Lunar Section members have long made use of the Orbiter imagery

in making their own topographic studies of particular areas/features of the

Moon. The list of papers in the Journal of the British Astronomical Association

on this work is a long one. People like Keith Abineri and Ivor Clarke have

made significant contributions. Keith Abineri’s work is legendary. I will

leave you to conduct your own literature search but one excellent paper by

Ivor Clarke: ‘A comparison of images from Orbiter IV and Clementine’, in the

August 1977 JBAAwill give you a good start (and he gives references to other

works).

These Orbiter images are available as prints. You can now also get

Clementine images on a set of 88 CD-ROMs and no doubt more and more

imagery will become available in computer media. For all NASA images and

information, write to: The National Space Science Data Centre (Americans

use the spelling ‘Center’), Co-ordinated Request and User Support Office,

World Data Center-A for Rockets and Satellites, Code 633.4, Goddard Space

Flight Center, Greenbelt, Maryland, 20771, USA, or contact them through

the Internet (see the next section).

Chapter 8 of this book is concerned with understanding the detailed

topography of the Moon in connection to its history and lunar science. You

will find a few examples of space-probe images of the Moon in Chapter 8

and some more in Chapter 6. Utilising spacecraft imagery will expand the

scope of your studies beyond that which is possible using your telescope

alone.

7.3 THE INTERNET

It is hard to think of things you cannot get on the Internet. Certainly infor-

mation and images about the Moon are in plentiful supply. Many (most?)

amateur astronomers/clubs and societies have their own sites and it is easy

to gain access to professional information and images – both from the

space missions as well as Earth-based observations. Web-site addresses tend

to be ephemeral, so it is a good idea to make a start by looking in publica-

tions such as the latest issues of the Journal of the British Astronomical

Association, the Handbook of the British Astronomical Association, and in Sky &

Telescope and other magazines for web-site addresses. Of course, you can

make use of the various search engines available – but do avoid typing in

146 THE DESKTOP MOON

‘mooning’! Many web sites have links to other web sites, so it should not

take much ‘surfing’ to uncover plenty of up-to-date information and

images.

One address that probably will not change before this book is in print

is NASA’s home page:

http//nssdc.gsfc.gov/

This is the National Space Science Data Center (NSSDC) at NASA Goddard

Space Flight Center, Greenbelt, MD 20771, USA.

Happy Moon surfing!

7.4 LUNAR EPHEMERIDES

Publications such as the Astronomical Ephemeris and the Handbook of the

British Astronomical Association provide useful ephemera for the lunar

observer and many societies and groups also provide hard-copy ephemera,

while the ubiquitous Internet probably has innumerable sites where this

information can be found (though it is wise to check on the accuracy of any

data given).

There are also plenty of programs available commercially, and some

available simply by downloading them from the Internet. Some, such as

‘Lunar Calculator’ (see the January 1999 issue of Sky & Telescope for a review)

are highly sophisticated, have vast databases, and can do things such as

simulate the views of the Moon that you would get from an orbiting space-

craft. Others present you with Earth-based views taking libration into

account, as well as providing you with much useful information such as

lighting angles, etc. New and improved software is continuously coming on

the market, so I will leave you to search out for yourself the up-to-date

advertisements and reviews and obtain the product that best suits your

own needs.

7.5 MEASURING LUNAR SURFACE HEIGHTS

When studying the Moon through your telescope you might wonder about

the relative heights of the lunar surface features. A crater might seem very

deep when near the terminator and largely filled with black shadow. On

the other hand it seems very shallow when the Sun rides high overhead.

What is the true depth of the crater? Which parts of it are above, and which

below, the surrounding moonscape? How high are the lunar mountain

peaks?

With some effort and a good deal of care you can find out for yourself.

The way to determine relative heights on the surface of the Moon is by

measuring the length of the shadows cast by features onto their surround-

ings.

7.5 MEASURING LUNAR SURFACE HEIGHTS 147

I must ‘come clean’ and say that the scientists processing the space-

probe imagery have been there before you. You will be undertaking this

task for your own gratification and your results will not generate any new

knowledge for the scientific community.

At one time the amateur astronomer would use a good eyepiece

micrometer on an 8-inch (203 mm) or larger telescope to measure heights

on the Moon. Nowadays, the amateur would be best advised to use high-

quality photographs and CCD images. Having said that, the November 1998

issue of Sky & Telescope carries an article ‘The Mountains of the Moon’ in

which a contemporary enthusiast, Bill Davis, describes how he makes

measurements at the eyepiece of his 8-inch Schmidt–Cassegrain telescope

using an eyepiece micrometer. I recommend reading this article if you are

interested in this sort of work. Also, I describe the use of an eyepiece

micrometer for lunar shadow measurements, and other projects, in my

book Advanced Amateur Astronomy (Cambridge University Press, 1997).

Owing to the limited space, I will here assume that either you are famil-

iar with the eyepiece micrometer or that you have sought out the refer-

ences given and will confine myself to explaining how to get the desired

height value(s) from your measurements. Where I refer to distances meas-

ured by eyepiece micrometer these can, of course, just as well be distances

measured by ruler on a photograph, etc. Here I will give the procedure to

be used with the eyepiece micrometer, since it can easily be adapted to

making measurements on a hard-copy image, while the reverse process is

certainly not so obvious.

The reduction procedure I describe herewith is only applicable to obser-

vations/photographs/CCD images made from the surface of the Earth.

As with most linear measurements at the telescope eyepiece, you

should use the highest magnification that the seeing permits. The microm-

eter’s transverse fixed wire is aligned along the shadow and the movable

wires are positioned to intersect the end of the shadow and the feature

(mountain peak, etc.) that is causing it. The drum reading(s) and the known

value of the micrometer constant are then used to calculate the apparent

length of the shadow in arcseconds. The measurement can be repeated a

number of times in order to increase the accuracy as well as to provide a

figure for the likely uncertainty in the calculated value (from the spread of

readings). However, you should remember that lunar shadows change their

lengths very rapidly, especially with the terminator nearby, so try to get the

measurements all done in a few minutes.

You will need to know the scale of the image (arcseconds per milli-

metre) if you are making direct measures from hard-copy images. You will

also need to know the date and time of the image so that you can look up

ephemeris data, without which you cannot make the calculation.


The apparent length of the shadow is then expressed as a fraction of the

Moon’s semi-diameter in the same units (arcseconds). This new quantity is

s. As an example, if the semi-diameter of the Moon at the time of the obser-

vation (this can be found in an ephemeris, such as The Astronomical

Ephemeris) was 1000 arcseconds and the measured value of the shadow was

3 arcseconds, then the value of s�0.003.

With the measurement completed, you can go on to calculate the

height of the lunar feature relative to the ground its shadow falls on by

using four equations. You will need some more values from an ephemeris

and from a lunar atlas (or other source of lunar latitudes and longitudes).

For convenience, I will now list all of the terms you need in the equations:

s�length of shadow/Moon’s semi-diameter

Lp�longitude of peak casting the shadow

bp�latitude of peak casting the shadow

colong�Sun’s colongitude

bS�Sun’s latitude

LE�longitude of Earth

bE�latitude of Earth

X, the distance of the apparent centre of the Moon’s disk to the sub-solar

point, may be found from:

cosX�sinbS · sinbE�cosbS · cosbE · sin(colong � LE). (7.1)

The apparent length of the shadow then has to be corrected for the angle

the Sun makes to the east–west plane:

S�s/sinX, (7.2)

where S is the corrected shadow-length expressed as a fraction of the

Moon’s semi-diameter. The altitude, A, of the Sun (measured in degrees) as

seen from the peak casting the shadow is found from:

sin A�sinbS · sinbp � cosbS · cosbp · sin(colong � Lp). (7.3)

At long last we can arrive at the height H, of the peak, expressed as a

decimal fraction of the Moon’s semi-diameter:

H�S sin A � 1⁄2 S2cos2A – 1⁄8 S4cos4A. (7.4)

Multiply H by 1738 and you have the height of the peak casting the shadow

expressed in kilometres.

In truth there is another correction that should be applied: the effect

of parallax since the ephemeris figures are geocentric (as seen from the

Earth’s centre) but your observed measurements are topographic (as made

from the Earth’s surface). However, the likely instrumental and human

7.5 MEASURING LUNAR SURFACE HEIGHTS 149

errors in the measurement are larger than the error generated by ignoring

this correction.

The instrumental and human errors will have their greatest effect

when measuring short shadows. Unfortunately, measuring long shadows

(the lunar feature then being near the terminator) will also give rise to a

large uncertainty in the height determination because the shadow will fall

across ground which itself varies in height. Ideally, one should make a

series of measurements over a range of lighting angles. In that way a profile

of the area can be generated.

Other methods of lunar height determination and explanations of

different reduction procedures can be found in The Observer’s Guide to

Astronomy, edited by Patrick Martinez and published by Cambridge

University Press in 1994.

7.6 MAPS, GLOBES, POSTERS AND CHARTS

I mention many of the pre-Apollomaps and charts of the Moon in Chapters

3 and 4. All these will be difficult to obtain. Though it is just possible that

you might come across one or more by way of the second-hand market,

national astronomical society libraries and/or the national inter-library

loan service are more likely to turn up a few of them.

Of the products currently available, quite a few are obtainable through

Sky Publishing at: Sky Publishing Corp., 49 Bay State Road, Cambridge, MA

02138, USA. I have taken the following details from their 1999 Catalogue

(of course, you can obtain most of these items elsewhere but it is always a

handy thing to do your shopping under one roof!):

Atlas of the Moon, by Antonin Rükl. Contains 76 labelled airbrushed

maps of the Moon’s near side and includes 50 close-range

photographs.

Exploring the Moon through Binoculars and Small Telescopes, by E. H.

Cherrington. A 229-page book which “reviews every major feature in

28 night-by-night chapters, with lots of black and white

photographs”.

Moon Map. Sky Publishing’s own map. 101⁄2 inches in diameter, with

300 named craters and other named formations. Only a small map

but it is orientated with south uppermost to match the view in

most astronomical telescopes from the Earth’s northern

hemisphere.

Mirror-Image Moon Map. Same as the previous map but it has been

mirror-reversed to match the view through a telescope with an odd

number of reflections (e.g. a Schmidt–Cassegrain with a star

diagonal in place).

Moon Poster. Two large (about 50 cm diameter) side-by-side views of the


Moon, near-side and far-side, produced by the National Geographic

Society. Includes several hundred named features.

Lunar Quadrant Maps. Produced by the Lunar and Planetary Laboratory,

at the University of Arizona, contains thousands of named and

designated formations and depicts all craters of more than 3.3 km

diameter. Set consists of four maps, each about 23 by 27 inches.

NASA Moon Globe. A detailed 12-inch globe, that comes with a plastic

base/stand and a booklet.

I must admit that I have no personal experience of the adequacy, or other-

wise, of any of these items, though Sky Publishing is a very reputable

company selling many high-quality wares (and, no, I do not have any vested

interest in the company!).

Another item untested by me is the Hatfield Photographic Lunar Atlas, as

the manuscript for my book had to be with the publisher before the atlas

was published by Springer–Verlag. I gave details about it in Chapter 4.

However, I am very familiar with its 1968 edition. Certainly I can attest to

the usefulness of that one and I await the new edition with anticipation.

You can often find Moon maps presented in general astronomy books,

though they often tend to be limited in size and the details they carry.

One fairly good example, containing simple geological maps of the Moon

as well as larger-scale topographic maps, is The NASA Atlas of the Solar

System, by Ronald Greeley and Raymond Batson, published by Cambridge

University Press in 1997. Norton’s Star Atlas, edited by Ian Ridpath, published

in its nineteenth edition by Longman in 1998, contains a reasonably good

photomosaic Moon chart.

Of course, computer media have the potential for the most detailed and

accurate Moon charts. For instance, there is the Lunar Digital Image Map

available from the NSSDC. It comprises a set of 15 CDs produced from

images taken by the Clementine spacecraft. Disks 1–14 contain mosaics cov-

ering the Moon at a resolution of about 100 metres per pixel. The last disk

contains global mosaics at resolutions of 0.5, 2.5, and 12.5 km per pixel.

Some other computer media have already been mentioned – but new prod-

ucts are continually coming onto the market, so I urge you to shop around

when you come to make purchases for yourself.

7.7 KEY MAP FOR CHAPTER 8

Chapter 8, occupying about half the length of this book, is given over to a

detailed study of a representative selection of 48 principal areas/features

(many others detailed along with each of these) on the Moon’s near-side,

the treatment being slanted to the interests of the telescopist. Herewith

(Figure 7.1) is a key map intended to help you locate each of the numbered

features.

7.7 KEY MAP FOR CHAPTER 8 151


Figure 7.1 Key map of theMoon, for use withChapter 8.

KEY:1. Agarum,

Promontorium2. Albategnius3. Alpes, Vallis4. Alphonsus5. Apenninus,

Montes6. Ariadaeus, Rima7. Aristarchus8. Aristoteles

19. Bailly10. Bullialdus11. Cassini12. Clavius13. Copernicus14. Crisium, Mare15. Endymion16. Fra Mauro17. Furnerius18. ‘Gruithuisen’s

Lunar City’

19. Harbinger,Montes

20. Hevelius21. Hortensius22. Humorum, Mare23. Hyginus, Rima24. Imbrium, Mare25. Janssen26. Langrenus27. Maestlin R28. Messier

29. Moretus30. Nectaris, Mare31. Neper32. Pitatus33. Plato34. Plinius35. Posidonius36. Pythagoras37. Ramsden38. Regiomontanus39. Russell

40. Schickard41. Schiller42. Sirsalis, Rima43. ‘The Straight

Wall’ (RupesRecta)

44. Theophilus45. Torricelli46. Tycho47. Wargentin48. Wichmann

The numbers on the map, and the key to it, follow the same sequence

as the numbers and titles of each of the sections in the next chapter. For

instance, number 4 on the map corresponds to number 4 in the key and is

named as ‘Alphonsus’. Look up ‘Section 8.4’ in the next chapter and you

will find it is headed ‘Alphonsus’.

In practice, you will normally use the system the other way round. You

might be reading Section 8.15 in the next chapter, about Endymion. To find

out where Endymion is you can look up number 15 on the map. Of course,

it is also named in the key presented with the map.

I do not pretend that the map is anything other than the simplest

guide. If you have a more detailed atlas or map to hand you probably will

not bother with this one. There is certainly not enough room for anything

more detailed in this book. On the other hand, it seemed a pity not to

include even the simplest aid to locating the features discussed in the next

chapter.

7.7 KEY MAP FOR CHAPTER 8 153

CHAPTER 8

155

‘A to Z’ of selected lunar landscapes

In the earlier chapters of this book, alongside the descriptions of observa-

tional hardware and techniques, I have tried to provide a picture of the

Moon and of lunar science past and present. Necessarily this ‘picture’ has

been painted with a rather broad brush. To really get to know the Moon,

one must be prepared to examine it in finer detail. To that end, this chapter

presents a selection of 48 specific features/areas of the Moon. Taken

together, these provide a representative selection of the types of lunar for-

mation one may encounter at the eyepiece of one’s telescope.

Why the particular selection that follows? I can only say that this has

been my personal choice. I have tried to cover the fullest possible range of

lunar features. You will find descriptions of craters both grand and small,

conventional and unusual in their profile. Mountains, valleys, domes, rilles

(both sinuous and linear), mare flood-plains and other types of terrain are

also described. In some of the sections broad areas are described. A few sec-

tions concentrate on particular features of special interest. Altogether,

over two hundred named formations are examined. Many are the ‘old

favourites’ of novice and experienced observers. Others are more ‘off the

beaten track’. Sometimes I have provided detailed descriptions. Other

times I have only provided sketchy details and leave you, the reader – and

I hope the observer, to find out things for yourself.

In some cases the features described provide an object lesson in partic-

ular observational techniques and/or pitfalls for the unwary. Others exem-

plify particular points of lunar science and geology. All are also of interest

in their own right. Everything is described from the viewpoint of the

observer with his/her backyard telescope. I have tried to provide a range of

targets for the full range of observers, from novice to advanced. My aim

is that you will be able to go to the telescope and interpret what you

see/photograph/image in terms of lunar science (and particularly lunar

evolution).

Look at page 152 and you will see a simple key map which may be of use

to you in locating the areas/features on the Moon’s face described in this

chapter. As previously explained, simply use the section number to locate

the item on the map. As an example, the principal feature described in

Section 8.26 (Langrenus) will be located at the point labelled 26 on the map

(also it is named against the number 26 in the key presented with the map).

At the head of each section I give the selenographic latitude and longitude

of the principal named formation. This immediately tells you in what quad-

rant you will find the formation on the key map. Going beyond that, even

the roughest estimate of position based on the latitude and longitude

figures will easily and quickly enable you to find the numbered formation

on the key map.

Of course, the latitude and longitude figures will also be of use in locat-

ing the formation/area on other Moon maps and atlases – the key map is

only intended as an aid to locating the main features discussed here. You

will undoubtedly want a much more detailed map/atlas for general use (see

the previous chapter).

Let me entice you to take the first steps of a journey of exploration. After

taking those first steps with me, I hope that you will then want to continue

on your own. The Moon you will discover is both a thrilling and an eerie

place of spectacle and wonder . . . .

8.1 AGARUM, PROMONTORIUM [14°N, 66°E]An impressive cape, projecting into the Mare Crisium, the highest peaks of

which reach up to several thousand metres above the mare. From time to

time there have been claims of apparent mistiness around the cape, espe-

cially to the south, and most frequently soon after local sunrise. The visibil-

ities of some of the tiny craters on the mare in the vicinity also seem

variable. I think that these appearances are probably not true Transient

Lunar Phenomena (TLP, see Chapter 9), but local variations of albedo with

Sun-angle. Why not make a long-term study of this area in order to estab-

lish its true behaviour as the Sun rises over it? As explained more fully in

Chapter 9, in TLP research it is particularly valuable to establish the true

apparent behaviour of lunar surface features as lunations progress and

under varying conditions.

Figure 8.1 is centred on the cape. It was taken using the 1.5 m reflector

at the Catalina Observatory (of the Lunar and Planetary Laboratory,

University of Arizona) on 1966 April 6d 7h 18m UT. At that time the seleno-

graphic colongitude was 96°.9.

156 ‘A TO Z’ OF SELECTED LUNAR LANDSCAPES

157

Figure 8.1 PromontoriumAgarum. Details in text.(Catalina Observatory pho-tograph – courtesy Lunarand Planetary Laboratory.)

158

Figure 8.2 Albategnius(centre) and Hipparchus(lower). Details in text.(Catalina Observatory pho-tograph – courtesy Lunarand Planetary Laboratory.)

8.2 ALBATEGNIUS [11°S, 4°E] (WITH KLEIN AND HIPPARCHUS)This 136 km diameter crater is very old, as witness its heavily degraded walls

and the intrusion of other craters into it, notably the 44 km diameter Klein

on its western (right in Figure 8.2) side. Moreover, the floors of both these

craters have been flooded with mare-type lavas. Notice how the lofty (and

unusually massive, for this size of crater) central peak of Albategnius pokes

up through the lava, as does the smaller central peak of Klein. Also notice

that Klein has degraded Albategnius and not the other way round. So, we

can conclude that Klein is younger than Albategnius. What is your opinion

about the age of the small crater that has intruded into the north-east rim

of Klein? Yes, I know the answer is fairly obvious. I deliberately chose this as

an easy example. The point is that you have made a start in unfolding the

dynamic history of the lunar surface.

North of Albategnius (near the bottom of Figure 8.2) lies the even might-

ier and more complex and more ancient Hipparchus. Hipparchus’s heavily

degraded (almost destroyed along its western section) rim spans 151 km.

Notice the almost parallel set of great scars cutting through the terrain in

this region of the Moon. Each channel is orientated, roughly speaking,

from south-south-east to north-north-west. Other examples exist in the

area further west than is covered by Figure 8.2. If you relish a challenge try

to deduce the history of this tortured area of the Moon’s surface, using

spacecraft (Orbiter, Clementine, etc.) images and, perhaps, your own tele-

scopic observations. I guarantee that you will be kept busy for a great many

hours! To get you started, backtrack the scars northwards and you will find

them to be radial to a particular major feature on the surface of the Moon.

Enough said?

The photograph was taken with the 1.5 m Catalina Observatory telescope

on 1966 September 6d 11h 7m UT, when the selenographic colongitude was

167°.5.

8.3 ALPES, VALLIS [CENTRED AT 49°N, 3°E]Even when seen through a small telescope, the ‘Alpine Valley’ (properly

called Vallis Alpes) is a truly striking spectacle around the times of first and

last quarter Moon. This tremendous gorge, nearly 180 km long, seems to

slice straight through the Montes Alpes, linking the Mare Imbrium with

the Mare Frigoris.

Certainly it is not simply a channel cut through the mountains by a

river of lava. I think that there is probably a connection between this

feature and the heavy linear scars that cross the highlands in the vicinity

of Albategnius and Alphonsus (see Sections 8.2 and 8.4). Perhaps all of

these great valleys were really formed by slumping of the crust along

stress fractures as a result of a very slight horizontal expansion of the

lunar mantle (or at least the deeper layers of the crust) after the regolith

8.3 ALPES, VALLIS 159

had first solidified? The most likely explanation, though, is that the

crust has shrunk very slightly after its initial solidification and stress

fractures developed as a result, with the ground slumping into each

fracture.

This type of formation is known as a graben. Perhaps the colossal

impact event that created the Imbrium basin was responsible for the

faults that ultimately produced the graben? Search through the Montes

Alpes and you will find other linear features that are at least approxi-

mately radial to the Mare Imbrium, lending support to this idea. However

none of these other linear features are anything like as strikingly obvious

as Vallis Alpes.

Certainly, though, the floor of the Vallis Alpes has been flooded with

lava. Also, a sinuous rille meanders along the length of the floor of this

great lunar valley. Perhaps a further, minor, episode of lava flowing after

the main formation and flooding processes were over? Under appropriate

illumination and excellent seeing conditions the rille can be seen in a

13 cm refractor of first-class optical quality. However, it is elusive and you

need not doubt your abilities if you fail to see it even when using a more

powerful telescope.

The view of the Vallis Alpes shown in Figure 8.3 was taken using the

Catalina Observatory 1.5 m reflector on 1967 January 20d 01h 45m UT, when

the Sun’s selenographic colongitude was 18°.4.


Figure 8.3 Vallis Alpes(centre) cuts throughMontes Alpes in thisCatalina Observatoryphotograph. Details intext. (Courtesy Lunar andPlanetary Laboratory.)

8.4 ALPHONSUS [13°S, 357°E] (WITH ARZACHEL, PTOLEMAEUS,ALPETRAGIUS AND HERSCHEL)

The three adjacent craters Arzachel (southernmost), Alphonsus, and

Ptolemaeus (northernmost) are very distinctive around the times of first

and last quarter Moon. The area is shown in Figure 8.4(a), the details of

which are the same as for Figure 8.2.

The 97 km diameter Arzachel is obviously the youngest of the three.

Even a small telescope is enough to show its richly complex structure. The

walls are heavily terraced and rise to a greater height (being about 4.5 km

above the immediate surrounds) on the eastern side than on the west

(height about 3.4 km – the surrounds being so rough and hummocky, these

figures are only very approximate).

The crater floor, itself lying nearly 1 km below the level outside the for-

mation, has obviously been partially flooded with lavas. Yet it is very far

from smooth. There are a number of small craters, several hills, and at least

one rille on the crater floor which are visible to the users of amateur-sized

telescopes. Note how much the ‘central’ mountain mass is offset from the

centre of the crater. All these features are well shown on the incredible

image obtained by Terry Platt (and shown in Figure 8.4(b)) using his 318 mm

tri-schiefspiegler reflector and Starlight Xpress CCD camera (other details

not available). I used Hauppauge ‘Image Editor’ software on my own com-

puter to further sharpen Terry Platt’s already outstandingly fine image.

Alphonsus is, arguably, one of the most interesting craters on the Moon.

This 119 km diameter ring-plain has highly complex walls and many fasci-

nating details can be made out on its flooded floor, especially by users of

large telescopes.

Look carefully at Figure 8.4(a) and you will see several small dark

patches on the floor of Alphonsus. At the centre of the patches are small

craters. These formations are known as dark halo craters. At one time these

were taken to be volcanic cinder cones, or fumaroles, and were used by the

supporters of the endogenic theory to bolster their views on the moulding

of the lunar surface. Apparent visual changes in these were even taken

as suspicions of some residual volcanic activity by a small minority of

researchers. However, the Apollo 17 astronauts visited an example of this

type of formation (a small dark halo crater named ‘Shorty’, on the south-

eastern border of the Mare Serenitatis) and found it to be a conventional

impact crater where the impact explosion had excavated dark mare

material from beneath a thin layer of lighter regolith. It is likely that the

other dark halo craters of the Moon have the same explanation.

Several rilles and faults cross the floor of Alphonsus. These are particu-

larly well shown in the superb image Terry Platt made of the crater and

which is presented in Figure 8.4(c) (subsequent image sharpening and

8.4 ALPHONSUS 161

162

Figure 8.4 (a) Arzachel(upper), Alphonsus(centre), and Ptolemaeus(lower) are the craters thatdominate this CatalinaObservatory photograph.(Courtesy Lunar andPlanetary Laboratory.)Details given in text.

(a)

other details as for (b)). The apparent changes in the dark halos are now

known to be variations in relative albedo with illumination angle.

As far as the controversial subject of Transient Lunar Phenomena (TLP)

is concerned, Alphonsus provided the best ‘hard-copy’ (as opposed to anec-

dotal) evidence that at least a small minority of the reported instances of

TLP are real events at the Moon’s surface and not simply illusions or mis-

takes on the part of the observers concerned. More on this in Chapter 9.

The northern section of the rim of Alphonsus merges with that of the

magnificent 153 km diameter ‘walled-plain’ Ptolemaeus. As one might

expect the terrain is highly chaotic and broken down at the merger,

8.4 ALPHONSUS 163

Figure 8.4 (cont.)(b) Arzachel – CCD imageby Terry Platt. Details intext.(c) Alphonsus – CCD imageby Terry Platt. Details intext.

(b)

(c)

Ptolemaeus pre-dating the formation of Alphonsus. The ancient flooded

floor of Ptolemaeus is covered in small craters and several crater-chains.

These are mostly rather delicate objects for those using moderate telescopes

under typical backyard conditions. The apparent brightness of the floor of

Ptolemaeus changes considerably during a lunation, as does the appear-

ance of the local ‘mottlings’ on it. The floor brightens considerably under a

high Sun, the Moon then being near full, but appears quite dark at times

close to first and last quarter Moon.

The area covered in Figure 8.4 overlaps that shown in Figure 8.2, which

lies to the east. Notice the same straight scars in the terrain, each hundreds

of kilometres long. What story do they tell? (There is no mystery but you

might like to deduce the answer for yourself. I offered a clue in Section 8.2).

The prominent 40 km diameter crater to the north-east of Alphonsus

and south-east of Ptolemaeus is called Alpetragius. Notice its prominent

central peak, rather ‘mound-like’ in profile. The walls of this crater are

rather finely terraced.

Of similar size to Alpetragius, and positioned just north of Ptolemaeus,

is Herschel. You might like to consider making a detailed comparison

between Alpetragius and Herschel. Given that the craters are similar in

many ways, why are they rather different in others?

8.5 APENNINUS, MONTES [CENTRED AT 20°N, 357°E] (WITH CONON,ERATOSTHENES, PALUS PUTREDINIS, SINUS AESTUUM, WALLACE)

If any feature on the Moon can take the prize for being the most striking

when seen through even the smallest telescope at the appropriate time,

then surely it has to be the magnificent Montes Apenninus. The “appropri-

ate time” for this formation occurs twice every lunation: near first and last

quarter Moon.

Spanning about 600 km along the south-eastern ‘shore’ of the Mare

Imbrium, this stunningly rugged mountain range strikes a breath-taking

spectacle when seen under a low Sun. I admit that I find the fine details

quite confusing when seen under good conditions with a powerful tele-

scope. I tend to use a higher magnification than I would normally do under

the ambient conditions just to enjoy the sheer awesome effect of the view.

This also reduces the confusion greatly. The slight softening of the image,

due to over-magnification, hardly matters when one gets the thrilling

impression of apparently flying over the complex array of mountain peaks,

ridges, and valleys!

Its origin dates back about 3850 million years, with the creation of

the Imbrium Basin. The impacting projectile caused the highland crust

along the south-eastern border to be violently uplifted, so forming the

range.


8.5 APENNINUS, MONTES 165

Figure 8.5 (a) The north-ernmost extent of theMontes Apenninus. Detailsin text. (CatalinaObservatory photograph –courtesy Lunar andPlanetary Laboratory.)

(a)

Figures 8.5(a) and (b) are sections of a photograph which was taken with

the Catalina Observatory 1.5 m reflector on 1967 January 20d 01h 46m UT,

when the Sun’s selenographic colongitude was 18°.5. Figure 8.5(a) shows

the mountain range to its northernmost extent. The conspicuous crater in

the midst of the mountain peaks (just to the right of centre of the photo-

graph) is the 22 km diameter Conon. The area of mare extending from the

bay a little north of Conon is called the Palus Putredinis (‘Marsh of Decay’).

Notice the extensive network of fine sinuous rilles in the area.

The Apollo 15 astronauts visited the north-eastern border of the Palus,

close to the foot hills of the Montes Apenninus and examined one of the

rilles (Hadley Rille) close-up.

Figure 8.5(b) shows the southernmost extent of the Montes Apenninus,

where it terminates with the prominent 58 km crater Eratosthenes. Under

a low angle of illumination Eratosthenes is particularly striking and, largely

shadow-filled, then appears to be very deep. The rim of the crater actually

rises to just over 2.4 km above the surrounding terrain level, while the floor

is depressed by about the same distance below the level of the outside sur-

rounds. A lunarnaut standing on the rim of the crater and looking towards

the central mountain complex would see the ground sloping away from


Figure 8.5 (cont.)(b) The southernmost ter-mination of the MontesApenninus with the craterEratosthenes (upper right).The ruined crater Wallacecan be seen near thebottom of this CatalinaObservatory Photograph.Details in text. (CourtesyLunar and PlanetaryLaboratory.)

(b)

him with an average gradient of about 1 in 3 (actually the walls are terraced)

down towards the crater floor (at a depth of nearly 5 km vertically below

that of the rim). The giant amphitheatre would be harshly sunlit, while the

sky above would be inky black. Imagine what a spectacle that would be!

Eratosthenes is somewhat of a lunar chameleon. Despite its stark mag-

nificence when seen at low Sun-angles (see also Figure 8.13(a), further on

in this chapter, where it appears alongside Copernicus), the crater takes

on a very ‘washed-out’ appearance when seen under a higher Sun. In fact

the crater can even give the completely illusory impression of then being

8.5 APENNINUS, MONTES 167

Figure 8.5 (cont.)(c) Eratosthenes and theSinus Aestuum, pho-tographed by Tony Pacey.Details in text.

(c)

filled with a white, pall-like, mist. Some other craters also show the same

optical behaviour and undoubtedly this has led to many a false claim of

TLP.

Some of the observers of yesteryear were convinced that changes regu-

larly happened within Eratosthenes (even the growth and dying of vegeta-

tion and the migrations of animal/insect life-forms!) but they were

certainly mistaken. Near full Moon Eratosthenes becomes really quite dif-

ficult to detect, especially as the ray system from the nearby major crater

Copernicus then tends to help with the camouflage.

Another notable feature, pictured in Figure 8.5(b), is the ruined crater

Wallace. Shown near the bottom of the photograph, the surviving remnants

of Wallace’s broken walls poke above the level of the Mare Imbrium. This

26 km crater has been almost entirely flooded by the lavas which filled the

old Imbrium Basin to form the Mare Imbrium about 3.3 billion years ago.

Figure 8.5(c) provides another view of Eratosthenes, this time almost

entirely filled with black shadow. It also shows off one of the more obscure

basaltic flood-plains to very good effect. This is the Sinus Aestuum, situated

to the immediate south-east of Eratosthenes. This ‘bay’ spans 230 km. It is

quite easy to trace the outline of the original basin that was to be later filled

with lava to form the sinus on this excellent photograph by Tony Pacey. He

used eyepiece projection to enlarge the image at the f/5.5 Newtonian focus

of his 10-inch (254 mm) Newtonian reflector onto FP4 film for this 0.5

second exposure on 1990 February 3d 19h 35m UT, when the Sun’s seleno-

graphic colongitude was 0°.4.

At higher Sun-angles the sinus becomes very hard to see. This is partic-

ularly so because the rays from the nearby Copernicus, splattered across

this region, then dominate.

Notice how the impact cut through, and obliterated, the southernmost

extent of the Montes Apenninus. Clearly the Aestuum impactor did its

work after the much more massive projectile that created the Imbrium

Basin had hit the Moon. As such, the Aestuum Basin must be one of the

youngest on the Moon, the Imbrium Basin itself being quite youthful.

What about the ages of Eratosthenes and the Imbrium and Aestuum flood-

plains relative to each other and the basins? The answer is well established,

and is quite easy to fathom but I will leave this as an exercise for you.

8.6 ARIADAEUS, RIMA [CENTRED AT 7°N, 13°E] (WITH ARIADAEUS,SILBERSCHLAG, JULIUS CAESAR, AND AGRIPPA)

Whenever the terminator lies in the vicinity of the Rima Ariadaeus this

rille becomes very easy to see even when using quite small telescopes.

Roughly 220 km long, it spans much of the rough terrain between the Mare

Tranquillitatis (to its east) and the junction between the Mare Vaporum (to

the north-west) and Sinus Medii (to the south-west).


169

Figure 8.6 (a) RimaAriadaeus. Details given inthe text. (CatalinaObservatory photograph –courtesy Lunar andPlanetary Laboratory.)

(a)

Figure 8.6(a) is a splendid view obtained using the Catalina Observatory

1.5 metre reflector, taken on 1966 May 27d 03h 56m UT when the Sun’s

selenographic colongitude was 356°.8. The whole area, especially to the

west, is rich in rilles and the right-hand side of Figure 8.6(a) also shows the

easternmost part of the famous ‘Hyginus Rille’, Rima Hyginus. Rilles make

a fascinating subject for study at the telescope eyepiece. Figure 8.6(b)

shows one such study made by Andrew Johnson. Details as written on the


Figure 8.6 (cont.)(b) Rima Ariadaeus drawnby Andrew Johnson.

(b)

drawing, but do note the orientation when comparing it to Figure 8.6(a).

Figure 8.6(a) is, in common with most of the other images in this book,

reproduced with south uppermost.

It may superficially look like a sinuous rille, except that it is rather

bigger and straighter, but Rima Ariadaeus is actually a graben – the vertical

slumping of ground along a stress fracture. Look carefully at Figure 8.6(a)

and you will see topographical features, such as mounds, along it that

clearly match the ‘high and dry’ features to either side. Notice that Andrew

Johnson has recorded some of these delicate features in his drawing which

shows the rille in the vicinity of the 13 km crater Silberschlag (which is also

shown near the centre of Figure 8.6(a)).

The easternmost extent of Rima Ariadaeus (far left on Figure 8.6(a)) is

marked by the small (11 km) bright crater Ariadaeus, notable for the intru-

sion of a smaller crater into it.

If you experience any trouble in locating Rima Ariadaeus, then first find

your way to the imposing 44 km diameter crater Agrippa (upper right on

Figure 8.6(a)) and the ancient ruined formation Julius Caesar (roughly

91 km in diameter and shown at the lower left of Figure 8.6(a)). Apart from

near full Moon you should easily be able to identify the rille passing

between these two craters and close to Silberschlag, which itself is conven-

iently half-way along a line between these two craters.

8.7 ARISTARCHUS [24°N, 313°E] (WITH HERODOTUS AND VALLIS

SCHRÖTERI)Even in the lowliest binoculars the crater Aristarchus stands out like a

brilliant diamond against the grey expanse of the Moon’s Oceanus

Procellarum. Aristarchus is the brightest of the large formations on the

lunar surface. It is quite easy to identify even when illuminated only by

Earthshine. Indeed, the great 18th Century astronomer William Herschel

mistakenly believed that Aristarchus was an erupting volcano! The crater

is reckoned to be very approximately 300–500 million years old. This is very

young for a Moon crater of its size. Its youthfulness is the reason for its high

albedo. The solar-wind bombardment has not had time enough to do its

work of darkening the materials excavated from below the regolith.

Aristarchus spans about 40 km from rim to rim and close inspection

reveals that it has a decidedly polygonal outline. It stands on an extensive

plateau, with the rim of the crater rising to over 600 metres above its

immediate surrounds. The interior terraced walls slope down to the

crater floor at a depth of some 2.1 km below the rim. As Figure 8.7(b)

shows, the appearance of the formation is somewhat confusing when

seen under a high Sun. With the terminator somewhat nearer the crater,

details then stand out readily: contrast Figure 8.7(a) with Figure 8.7(b).

8.7 ARISTARCHUS 171

172

Figure 8.7 (a) Aristarchus(the largest crater shown),Herodotus (right ofAristarchus) and VallisSchröteri (belowHerodotus) at colongitude63°.7. Details in text.(Catalina Observatory pho-tograph – courtesy Lunarand Planetary Laboratory.)

(a)

8.7 ARISTARCHUS 173

Figure 8.7 (cont.)(b) Aristarchus and envi-rons at colongitude 79°.3.Details in text. (CatalinaObservatory photograph –courtesy Lunar andPlanetary Laboratory.)

(b)

Both photographs were obtained using the Catalina Observatory 1.5 m

reflector: (a) was taken on 1965 December 06d 05h 14m UT and (b) was taken

on 1966 October 28d 06h 28m UT.

The youthfulness of Aristarchus has already been referred to in connec-

tion with its albedo. This characteristic also gives it a degree of thermal lag,

when it comes to the diurnal cycle. In the lunar mornings bright fea-

tures such as Aristarchus show up as cold spots on thermal maps, since

they reflect away more of the solar radiation. However, the reverse is the

case after sunset. Good reflectors make poor emitters. Then they show

up as being warmer than their surrounds. During the local lunar night

Aristarchus can remain up to 30 degrees Celsius warmer than its surrounds.

Another indicator of the youthfulness of Aristarchus is the complexity

and crispness of the terracing of its walls. Further evidence is provided by

its relatively complex floor and central mountain (features on the Moon

lose their ruggedness as time passes).

One intriguing feature of Aristarchus is readily apparent in Figure

8.7(a): the system of radial dark bands that extend up the interior terraces


Figure 8.7 (cont.)(c) Orbiter IV photograph ofAristarchus, Herodotusand Vallis Schröteri.(Courtesy NASA andProfessor E. A. Whitaker.)

(c)

of the crater. They were first drawn by Lord Rosse in 1863 but were not

recorded, nor even as much as mentioned, by the earlier observers of the

Moon. Why was it that the likes of Mädler, Schmidt, or Neison failed to dis-

cover the bands when these great selenographers paid considerable atten-

tion to Aristarchus? How could they possibly miss a striking feature that

even I as a novice observer could so readily see in my 76 mm reflector at the

beginning of the 1970s? Could the bands have gone from being very hard

to see to very obvious in the intervening century? I, for one, find this very

hard to believe. There is a real mystery here.

Take a look for yourself. You should easily be able to see the two most

prominent bands in a small telescope and you might count up to nine of

them if you use a large telescope under suitable lighting and good atmos-

pheric conditions. The bands do vary in intensity throughout the lunation,

being hardest to see when the terminator is close by. You might like to

make a study of their changing appearance.

The striking ray system emanating from Aristarchus tells a story about

the impactor that created the crater. As is usual for ray systems on the lunar

surface, the Aristarchus rays are most obvious when illuminated by a high

Sun. Figure 8.7(b) shows the ray system well. Rays radiate in all directions

from Aristarchus but note how the majority of the crater ejecta stream off

to the south-west. Clearly the projectile hit the Moon at a fairly low angle,

and came from the north-east. Look at the shape and offset of the interior

‘central’ mountain as shown in Figure 8.7(a) and you will find confirmatory

evidence for this hypothesis.

The Aristarchus plateau, already referred to, is an approximately square

area of rough and hummocky terrain, extending about 200 km�200 km.

Altimetry data obtained by the Clementine space probe reveals that the

southern edge of the plateau is about 2 km higher than the general level

of the Oceanus Procellarum and that it gently slopes downwards to the

north and north-west (the average slope being about one degree).

To me, the plateau seems to have a rich ‘coffee-brown’ tint that

contrasts strongly with the white Aristarchus and the greenish-grey

mare. As noted in Chapter 2, though, perceived colours are not accurate

(and not everybody’s eyes are colour-sensitive enough to show them)

but the colour contrasts are at the least instructive. Proper colori-

metric studies do, indeed, reveal that the plateau is much redder than

the average hue of the Moon. The multi-waveband images obtained by

Clementine indicates that the colour arises due to a layer of reddish pyro-

clastic glasses.

Other interesting features highlighted by Clementine include the pres-

ence of the mineral olivine distributed along the southern part of the rim

of Aristarchus and the presence of anorthosite on the crater’s central (or

near-central!) peak.

8.7 ARISTARCHUS 175

Sitting on the plateau, alongside Aristarchus, is the slightly smaller

and much shallower crater Herodotus. Both craters in effect at least

approximately define the southernmost boundary of the Aristarchus

plateau. The differences between the two craters could hardly be greater.

Herodotus is obviously an ancient crater whose floor has been lava-flooded.

Superficially the floor looks smooth but some craterpits are revealed by

large-aperture telescopes used under good conditions. Space-probe images

show the floor of Herodotus to be covered in tiny craters and fissures.

Perhaps the most remarkable feature in this very remarkable region of

the Moon is Schröter’s Valley, or more properly Vallis Schröteri. This is the

Moon’s largest sinuous rille, originating at its southernmost end at a deep

crater known as the Cobra’s Head and winding on for over 160 km to the

western corner of the Aristarchus plateau. The impression is that it was

created by a river of lava erupting from the Cobra’s Head and cutting its

way along a winding path to lower ground. Most lunar experts think that

this was, indeed, what happened. A finer sinuous rille runs along the

length of the floor of the valley, indicating at least one subsequent lava

flow. This is best seen in the Orbiter IV photograph presented in Figure 8.7(c).

The whole area abounds with finer sinuous rilles. Clearly the geologi-

cal (I would prefer to say ‘selenological’ but that term is not in fashion)

history of this region is very complex.

The area is especially interesting for those involved in the controversial

study of Transient Lunar Phenomena. About a third of all the catalogued

reports of TLP involve Aristarchus or its surrounds. It is the single most

‘event prone’ of the areas if one is to believe all the reports. However, it

must be borne in mind that the brilliance of Aristarchus may well be

responsible for many illusory reports. Especially so as spurious colour, the

prismatic splitting of colours along light–dark boundaries caused by the

Earth’s atmosphere, is especially evident with this crater. Often the south-

ernmost part of the rim, and extending to the southernmost boundary of

the ejecta blanket, shows a yellow or even orange-red glow due to this cause

(the complementary colour showing up chiefly along the northern rim of

the crater). Also there is the problem of observational selection. Being so

apparently ‘event prone’ observers tend to concentrate their efforts to stud-

ying this area, so distorting the statistical evidence. However, it is true that

there is some evidence for real TLP in this area and it may be significant

that the Apollo 15 particle spectrometer indicated a higher than average

emission of radon gas when it flew over Aristarchus.

Aside from the various effects which have been reported involving

Aristarchus itself, various reports of mistiness and coloured effects issuing

from the Cobra’s Head are on record. The transient event that I have most

faith in as being something genuine, of any of the very few that I have wit-


nessed myself, involved the crater Aristarchus. More about this and the

whole subject of Transient Lunar Phenomena in the next chapter.

8.8 ARISTOTELES [50°N, 17°E] (WITH EUDOXUS AND EGEDE)The crater Aristoteles stands proudly just south of part of the ‘shore’ of the

Mare Frigoris and a little way east of the Montes Alpes. It is 87 km from rim

to rim and possesses very finely terraced walls, rising to over 3.3 km above

the floor. The floor, itself, is far from smooth. A low Sun-angle reveals that

it is rippled with small hills. A little to the south lies the 67 km diameter

Eudoxus, itself laying at the northern termination of the Montes Caucasus.

It’s walls rise to a similar height as Aristoteles.

Aristoteles and Eudoxus are a magnificent pair of craters, easily iden-

tified at almost all lunar phases. Figure 8.8(a) shows the formations under

morning illumination, while Figure 8.8(b) shows them late in the lunar

day. Both photographs were obtained using the Catalina Observatory 1.5 m

reflector: (a) was taken on 1967 January 20d 01h 45m UT and (b) was taken

on 1966 September 04d 10h 03m UT. However, the terminator was not par-

ticularly close for either photograph. I will leave you to study the detailed

8.8 ARISTOTELES 177

Figure 8.8 (a) Aristoteles(lower crater) and Eudoxusare the largest craters onthis Catalina Observatoryphotograph taken atselenographic colongitude18°.4. The small, lava-flooded, crater to the rightis Egede. Other details intext. (Courtesy Lunar andPlanetary Laboratory.)

(a)

topography of the area (and I especially commend to you the arc of moun-

tain peaks which span Aristoteles and Eudoxus to the north) and to work

out the chronologies.

However, there is something I will draw to your attention: the highly

polygonal outlines of the craters. Notice how the small (37 km) flooded and

ruined crater Egede (situated just to the west of the arc of mountain peaks

just referred to) also shares the polygonal outline. Ask a casual observer

what are the shapes of the outlines of the lunar craters and the answer you

will probably get is that they are circular. Actually, many of them are decid-

edly polygonal. There is also some evidence that many of the faults on the

lunar surface are aligned in the same general directions as the distortions

to the crater outlines. This has been termed the lunar grid system, though

not everybody accepts its validity. Has some global twisting of the Moon

occurred in recent times (even some of the youngest craters have polygonal

outlines) to cause the distortion? This certainly seems highly implausible.

The mystery remains.


Figure 8.8 (cont.)(b) Aristoteles and environsat selenographic colongi-tude 142°.6. Other detailsin text. (CatalinaObservatory photograph –courtesy Lunar andPlanetary Laboratory).

(b)

8.9 BAILLY [67°S, 291°E]Under old terminology the largest craters were called ‘walled plains’, or ‘ring

plains’. Bailly, at 303 km diameter, qualified as the largest ‘walled plain’ on

the Moon’s Earth-facing hemisphere. Now, though, Bailly is regarded as one

of the smallest basins. Basins are spread over both hemispheres of the Moon

in approximately equal proportions but those on the Earth-facing side are

almost all flooded with mare basalts. By contrast, there is almost no mare-

type lava flooding on the Moon’s far side and so the basins there are still ‘raw’,

as is Bailly. The huge projectiles that created the basins belong to the early

history of the Moon. In all probability Bailly is more than 3 billion years old.

There are two probable, and connected, reasons why Bailly has

remained free of lava flooding. One is that the impacting projectile was

not massive enough (and so did not convey enough kinetic energy) to

cause sufficient fracturing of the Moon’s crust to drive fissures deep

enough to reach through to the upper mantle. Even near the centre of the

8.9 BAILLY 179

Figure 8.9 (a) Bailly spansthis Catalina Observatoryphotograph taken at aselenographic colongitudeof 80°.9. Details in text.(Courtesy Lunar andPlanetary Laboratory.)

(a)

Moon’s Earth-facing disk (where the crust is thinnest) the flooded plains

are all of greater diameter than Bailly. The second reason is that Bailly, like

the great basins of the Moon’s far side, is positioned over a region where

the crust is thicker than the average near the sub-Earth point.

Being so close to the south-western limb, Bailly is best observed just a

little before full Moon, when the crater experiences lunar morning. Even

then it can be badly affected by libration. The views of it at lunar evening

are often unsatisfactory since the Moon is then a very thin crescent, and so

is rather too close to the Sun in the sky to allow for good observing condi-

tions. It is probably because of this that the earliest selenographers missed

discovering Bailly. Cassini was the first to record it in his map of 1680.

Figure 8.9(a) provides a magnificent view of this huge formation. This

photograph was taken on 1966 January 06d 05h 45m UT with the 1.5 m reflec-

tor of the Catalina Observatory. The formation’s great age is evident by

its general state of ruin. Note how the ramparts have been smoothed and


Figure 8.9 (cont.)(b) Bailly is largely in dark-ness but part of the rim ofBailly B can be seen emerg-ing into the morning sun-light in this view taken ata selenographic colongi-tude of 61°.0. Other detailsin text. (CatalinaObservatory photograph –courtesy Lunar andPlanetary Laboratory.)

(b)

eroded, particularly by aeons of impacts. Even so, in places they still soar

upwards to over 4 km above the mean floor level!

When Bailly is on view and the conditions are suitable you might like

to examine it for yourself. You will find the floor of this formation littered

with myriads of craters and ridges. However, the foreshortening will always

prove a challenge to successful examination. Of the two large and overlap-

ping craters at the south-eastern rim of Bailly, the smaller is known as

Bailly A. It is 38 km in diameter and actually crosses the rim of Bailly. The

larger of the two was, for a time, known as Hare but has now reverted to its

original designation of Bailly B. Bailly B is very deep (over 4 km from rim to

floor) for its 65 km diameter.

Watching/drawing/photographing/imaging lunar formations as the ter-

minator passes over them is highly instructive. It is in this sort of activity

that the very few (and dwindling) possibilities for useful and original topo-

graphic study lie. Take a look at Figure 8.9(b). This is another Catalina

Observatory photograph but this one was taken on 1967 February 27d 03h 43m

UT at a slightly earlier lunar phase. This time the floor of Bailly is almost

entirely in black shadow. Notice, though, the rim of Bailly B catching the

morning sunlight. . . .

An ancient lunar formation full of fascination but a degree of dedica-

tion is needed in order to pursue its study at the telescope eyepiece.

8.10 BULLIALDUS [21°S, 338°E] (WITH KÖNIG, LUBINIEZKY AND

WOLF)Measuring just 61 km from rim to rim, Bullialdus may not be one of the

largest craters on the Moon but it makes up for that in being one of the

most beautifully formed.

Despite its small size, it is very easy to locate, sitting proudly and prom-

inently on the Mare Nubium. Figure 8.10(a) is a Catalina Observatory photo-

graph, taken with the 1.5 m reflector on 1966 December 23d 04h 54m UT. The

terraced walls (about 2.4 km in vertical height) are evident in the photo-

graph, as is the somewhat polygonal outline of the crater and its slightly

convex floor.

Bullialdus contains a wealth of detail to entertain and interest the

observer equipped with a moderate telescope. The central mountain mass

is complex and it changes its appearance quite considerably over the luna-

tion as the various shadows develop with changing Sun angle. Another

shadow effect concerns the crater floor. Under a low Sun in the local lunar

morning it tends to be dark and fairly evenly shaded (the effect of the con-

vexity accepted) but it brightens considerably as the Sun angle increases

and various dark markings appear, change shape and prominence, and

then fade as local sunset approaches. This effect is caused by the rough and

8.10 BULLIALDUS 181


Figure 8.10 (a) Bullialdusis the largest crater shownon this CatalinaObservatory photograph,taken at a selenographiccolongitude of 39°.9.Bullialdus A nearly joinsBullialdus and BullialdusB is just above this. At thetop, and over to the right,is König, whilst belowKönig and down at thebottom is Lubiniezky.Other details in text.(Courtesy Lunar andPlanetary Laboratory.)(b) Bullialdus is over to theright and is filled withshadow and Wolf is theprominent formation inthe upper left of thisCatalina Observatory pho-tograph, taken at a colon-gitude of 22°.6. Otherdetails in text. (CourtesyLunar and PlanetaryLaboratory.)

(a)

(b)

slightly lumpy nature of the crater floor, the individual shadows generated

within the surface relief being too small to appreciate individually but the

combined effect producing the behaviour that is noticeable through the

telescope.

Near the time of full Moon, the central mountain complex becomes

very bright as does much of the crater rim and the interior develops many

bright spots.

Away from the time of the full Moon, the careful observer may discern

some landslips and even some small craters in Bullialdus’s inner terraces.

Notice the lines of thin black shadow defining the terraces in the south-

west of the interior. Clearly here the steps slump backwards by several

degrees. The black spot at the southern end of this section can also become

very prominent, indicating a hollow. Under a higher Sun, a ridge, running

a short way radially down the terraces, becomes visible in the same loca-

tion. Look closely at Figure 8.10(a) and you should be able to discern an

intriguing raised ridge crossing south-east from the central mountain

complex to the foot of the wall terraces.

The outer surrounds of Bullialdus are also of particular interest. The

complex array of ridges, most of which are radial to the crater, and chains

of secondary craters and some blanket ejecta are visible in Figure 8.10(a).

Figure 8.10(b), another Catalina Observatory photograph – this one taken

on 1966 May 29d 04h 41m UT – shows some of these features to better effect,

here the interior of Bullialdus itself being filled with black shadow.

Almost abutting onto the southern rim of Bullialdus is the 26 km

Bullialdus A. The rough ground of their shared outer flanks is interesting.

Which crater do you think was formed first? The answer to that ought to

be fairly obvious but I will leave that as an exercise for you.

With a gap between their rims of very roughly 20 km, Bullialdus B lies

a little further south-south-west of Bullialdus A. Bullialdus B is 20 km in

diameter. It is instructive to compare the outlines of these smaller craters

with that of Bullialdus itself.

Roughly 80 km, or so, to the west-south-west of Bullialdus B we find the

similarly sized (23 km diameter) and even more polygonal König. It has a

slightly more ‘broken down’ appearance than Bullialdus A or B. All three

share slight central elevations and generally mound-ridden and pock-

marked interiors.

North-north-west of Bullialdus is the broken down and lava-flooded

crater Lubiniezky. The 44 km diameter walls are completely demolished in

the direction of Bullialdus, as is evident in Figure 8.10(a). Also an intriguing

bright streak crosses the floor of Lubiniezky, exactly aligned with a similar

streak running tangentially to the exterior of Bullialdus. Careful examina-

tion reveals this to be the brightest member of a whole pattern of closely

8.10 BULLIALDUS 183

spaced parallel light streaks in the locale, but most prominent in the inter-

ior of Lubiniezky. As might be expected, the ancient basalt lava covering of

Lubiniezky is ridden with craters but most of these pose a challenge to the

eyesight of an observer using even a large telescope in excellent conditions.

The upper-right section of Figure 8.10(b) shows a very peculiar forma-

tion, known as Wolf. I will leave this as a challenge for you to investigate,

along with the ghost ring which is visible near the middle top of the same

photograph. A thoroughly fascinating region of the Moon!

8.11 CASSINI [40°N, 5°E] (WITH THEAETETUS)Cassini is a rather striking crater situated on the Palus Nebularum and at

the southern head of the Montes Alpes. The northernmost extent of the

Montes Caucasus lies a short distance to the east. The crater is quite con-

spicuous at all but the highest Sun angles and so it is surprising that it

was not recorded by the earliest selenographers. Cassini was the first to

record it on his 1692 map. Just in case there should be any doubt, do let

me add that there is no suspicion, whatever, of it being a crater only just

over three centuries old! Dating the original impact precisely may well be

problematical but we are certainly reckoning in billions of years, not

mere centuries.

Figure 8.11(a) is a photograph centred on Cassini taken with the 1.5 m

reflector of the Catalina Observatory on 1966 September 06d 10h 44m UT,

when the Sun’s selenographic colongitude was 167°.3. Cassini, itself, is

57 km in diameter and has complex and rather broad outer ramparts. As is

obvious from the photograph, the crater has been partially filled with

mare-type lavas, presumably during the period of major flooding that filled

the Imbrium Basin about 3.3 billion years ago. However, the crater-forming

impact might conceivably have come a little after, perhaps resulting in fis-

suring of the still thin crust under the crater allowing a subsequent upwell-

ing of lavas.

Certainly, though, the floor of the crater is old, and consequently satu-

rated with small craters, together with a few larger examples. The largest of

these, Cassini A, is 15 km in diameter and is situated somewhat north of the

centre of Cassini. Near the south-western flank of the interior is the 9 km

diameter Cassini B. Other floor details include various hummocks and

ridges, as well as more, rather smaller, craters. The most delicate of these

are a test for an observer with a powerful telescope working under good con-

ditions. A good CCD image of Cassini is shown in Figure 8.11(b). It was taken

by Gordon Rogers on 1997 February 15d 00h 49m UT, using his 406 mm Meade

LX200 catadioptric telescope and Starlight Xpress CCD camera.

The nearest major crater to Cassini, of the order of a hundred kilome-

tres to the south-east and nestling close to the western foothills of the


185

Figure 8.11 (a) Cassini(centre) and Theaetetus(upper left of Cassini).Details in text. (CatalinaObservatory photograph –courtesy Lunar andPlanetary Laboratory.)

(a)

Montes Caucasus, is Theaetetus. It is about 25 km in diameter but its

outline is obviously rather distorted. The rim of Theaetetus rises some 600

metres above the level of the outer surrounds but the floor of this crater is

at a depth of over 2 km below the rim. It possesses a small, rather low,

central mound. The terrain to the north and to the east of this crater is

highly complex.

The occasional odd appearance has been reported in the vicinity of

Theaetetus, by W. H. Pickering and by other observers. In 1902 the French

astronomer Charbonneaux, using the 830 mm refractor of the Meudon


Figure 8.11 (cont.)(b) Cassini – CCD image byGordon Rogers. See text fordetails.

(b)

Observatory, recorded the formation of a temporary “white cloud” near the

crater and in 1952 Patrick Moore, using his 121⁄2-inch (318 mm) Newtonian

reflector, saw “a hazy line of light” crossing the otherwise shadow-filled

interior of the crater.

8.12 CLAVIUS [58°S, 345°E] (WITH PORTER, RUTHERFURD, CLAVIUS C,D, J, K, L AND N)

A huge formation in the Moon’s southern highlands, Clavius is surely one of

the best known and easiest lunar formations to identify. It is a great crater,

of the type that used to be called a ‘walled plain’, some 225 km in diameter.

At a lunar phase of about 8–9 days (selenographic colongitude about

17°) it is entirely filled with black shadow. At these times you only need

good eyesight, and no optical aid, to see it as a distinct notch in the termi-

nator. Sunrise over the formation is spectacular, with the central regions

coming into view first. Andrew Johnson captures something of the grandi-

osity of the scene in his drawing, which is shown in Figure 8.12(a). This

demonstrates that the floor of the crater, though rough and cluttered with

detail, does at least follow the general curvature of the Moon’s surface. In

fact, it would not be at all obvious to a hypothetical observer stationed

within Clavius that he was inside a crater at all. From the centre he could

not see the walls and if he was in sight of one wall he could not see its con-

tinuation round to the other side of the crater.

Figure 8.12(b) is a Catalina Observatory photograph which shows the

formation under a slightly higher Sun angle than the view shown in (a). It

was taken with the 1.5 m reflector on 1967 January 20d 01h 52m UT, when

the Sun’s selenographic colongitude was 18°.5.

Clavius seems to be of Nectarian age. In other words, it is somewhere

around 4 billion years old. Hence it slightly pre-dates the Mare Imbrium

and the global flooding of the large basins which formed the lunar maria.

However, I would bet that it is slightly younger than Bailly. I will leave you

to make a detailed comparison of Bailly and Clavius for yourself.

Although the official classification of a basin is reserved for forma-

tions larger than 300 km across, there can be little real doubt that Clavius

is just a smaller example of the same. The walls of Clavius rise but little

above the outer surrounds. Indeed, to the south they are heavily broken

down and here the rim is rather ill defined. This formation is really a

great trough sunk over 3.5 km below the outer surface. The nature of the

walls vary somewhat going round the crater. From the north and going

round to the west the terracing is coarse and broad, becoming narrower

and more cliff-like round to the south. The very complicated and hum-

mocky nature of walls bordering the rest of the crater is evident in Figure

8.12(b).

8.12 CLAVIUS 187

Apart from its size, the most striking feature of Clavius must be its

interior craters. Starting with the 48 km Rutherfurd (shown on the oldest

maps as Clavius A) an arc of craters of decreasing size curves across the floor

of Clavius. Clavius D is next, diameter 28 km, then C (21 km), N (13 km), and

J (12 km). These are the main ones forming the arc of craters but smaller

examples abound, tending to form a closed loop which doesn’t quite reach

the south-western ramparts of Clavius but curves back towards Rutherfurd.

Of course, this closed loop is only approximately circular and is very


Figure 8.12 (a) Claviusdrawn by Andrew Johnson.(a)

roughly defined when we are considering the smallest craters. The whole

effect is, nonetheless, striking and supporters of the endogenic theories of

crater formation made much of Clavius and its interior craters as evidence

to support their views. It is not hard to see why.

I find it very difficult to accept that the formation of Clavius’s interior

craters is the product of purely random impacts. However, I am certainly

not advocating the abandonment of the impact theory of crater formation!

It is just that I think the situation involving Clavius is a little more

involved. Could it be that the impactors arrived together and in some sort

of formation? That is perhaps not as fantastic as it sounds. One might envis-

age a partially fragmented asteroidal or cometary body slamming into the

already formed great ring of Clavius itself. Having said that, there is one

difficulty. The craters show signs of not being the same age – at least as

regards their ejecta patterns. Clavius D looks to be the youngest. However,

the morphology of the area is highly complicated and so the age differ-

ences might be illusory. I must here emphasise that the official view is that

the arrangement of craters within Clavius is purely a chance one. Whatever

the truth, Clavius is certainly not one of the easiest of lunar formations to

investigate!

8.12 CLAVIUS 189

Figure 8.12 (cont.)(b) Clavius (CatalinaObservatory photograph –courtesy Lunar andPlanetary Laboratory.)

(b)

Even if the foregoing idea of a single fragmented body creating the

curve of interior craters of Clavius is correct, then Rutherfurd was probably

not included in this great event. The reason I say this is that Rutherfurd,

unlike the others so far mentioned, shows definite signs of being created

by an oblique-angle impact. It has the offset central peak, other interior

details, and ejecta pattern (admittedly faint and hard to discern) that

suggest a low-angle impact from the south-east. In addition to the details

mentioned previously, the interior of Rutherfurd is complex and rather

untypical of that of craters of its size. Sets of ridges radiate outwards from

the rim of Rutherfurd across part of the floor of Clavius.

While Rutherfurd spans the rim of Clavius to the south-east, Porter

does the same in the north-east. At 52 km diameter it is slightly larger than

Rutherfurd and is noticeably non-circular. It, too, has a rather complex and

hummocky interior and hummocky outer ramparts. On the oldest maps

Porter is referred to as Clavius B. Other large craters ‘splashed’ into the rim

of Clavius are Clavius L (diameter 24 km) to the west and Clavius K (diame-

ter 20 km) to the south-east of Clavius L.

One oddity is that the floor of Clavius has some smoother areas, mostly

in the east. Perhaps the impact events that created Rutherfurd and Porter

are responsible for this. However, could a degree of volcanism have played

a part in the early history of Clavius? Spectacular as it is when seen even

through the smallest of telescopes, there is much about Clavius that we do

not yet fully understand.

8.13 COPERNICUS [10°N, 340°E]One early example of satire, and surely the only one to involve a heavenly

body, must be Riccioli’s naming of the lunar crater Copernicus in the seven-

teenth century. He detested the very idea of the Earth being in orbit around

the Sun, as championed by Nicolaus Copernicus a century earlier. So he, in

his own words, “flung Copernicus into the Ocean of Storms”.

Sited prominently on the expanse of the Oceanus Procellarum as the

crater is, Riccioli could hardly be accused of trying to ‘bury the opposition’.

In fact, now we know that the Solar System really is Sun-centred, it is fitting

that one of the most prominent of the lunar formations bears the name of

Copernicus. I wonder what Riccioli’s reaction would have been if he could

have known how his raillery was to so spectacularly backfire!

In their 1874 book The Moon, Nasmyth and Carpenter wrote of the crater

Copernicus:

This may deservedly be considered as one of the grandest and mostinstructive of lunar craters. Although its vast diameter (46 miles) is exceededby others, yet, taken as a whole, it forms one of the most impressive andinteresting objects of its class. Its situation, near the centre of the lunar disc,


renders all its wonderful details, as well as those of its immediatesurrounding objects, so conspicuous as to establish it as a very favouriteobject.

Few can disagree with their opinion on the matter. T. G. Elger, the noted

observer of the Moon, author of a Moon book, and first Director of the

Lunar Section of the British Astronomical Association, christened the

crater Copernicus “the Monarch of the Moon”.

8.13 COPERNICUS 191

Figure 8.13 (a) Sunriseover Copernicus (the right-hand crater), photographed by TonyPacey on 1992 February12d 21h 35m UT, using his10-inch (254 mm) f/5.5Newtonian reflector. Theimage was projected toabout f/50, using an eye-piece, onto T-Max 100 filmand a 0.5 second exposuregiven. The film was pro-cessed in HC110 developer.The Sun’s selenographiccolongitude was 22°.3 atthe time of the exposure.The crater on the left ofthe photograph isEratosthenes, describedwithin Section 8.5.

(a)

192

Figure 8.13 (cont.)(b) Copernicus pho-tographed using the 1.5 mCatalina Observatoryreflector on 1967 January21d 02h 44m UT, when theSun’s selenographic colon-gitude was 31°.4.

(b)

The modern value for the diameter of Copernicus is 93 km. Just before

first and last quarter Moons the crater is entirely filled with black shadow.

Figure 8.13(a) shows the Sun beginning to rise over the formation, as photo-

graphed by Tony Pacey. More and more of the spectacular interior of this

crater is revealed as the Sun rises higher and the shadows retreat to the

eastern flanks until views such as that shown in Figure 8.13(b) are displayed.

The first thing to notice is that the outline of the crater is far from being

perfectly circular. It consists of roughly linear sections of varying lengths,

8.13 COPERNICUS 193

Figure 8.13 (cont.)(c) Copernicus drawn byAndrew Johnson.

(c)

broken again by irregularities on the smaller scale. This polygonal outline

is at least approximately carried down towards the crater floor by the

complex system of terraces. These were created by the rebounding and

interfering shock waves during, and in the immediate aftermath, of the

colossal explosion that created the crater (which has been estimated to be

of magnitude equivalent to about 20 trillion tons of TNT). The terraces

themselves are not the sharply cut steps they appear to be in small tele-

scopes but are somewhat rounded and softened into mounds and ridges.

Andrew Johnson represents this appearance in a drawing he made using

his 210 mm reflector, and which is shown in Figure 8.13(c).

The terracing of Copernicus also shows evidence of some slumping in

places. This can best be seen in Figure 8.13(d) which shows one of Terry

Platt’s incredible CCD images. Note that the Sun angle is higher for this

view, revealing more details of the eastern part of the crater interior.

The floor of the crater is an almost circular plain about 62 km in diam-

eter and lies 3.8 km below the crater rim and about 2.9 km below the

general level of the outer surrounds. It has a central mountain complex,

comprising of several peaks in an arrangement which extends in a roughly

east–west direction. The highest of the peaks reaches up about 1.2 km

above the crater floor. The southern part of the crater floor is noticeably

rougher than the northern section.

The outer slopes of Copernicus are complex, with a chaotic terrain of

mounds and radial ridges and crater ejecta. In fact, Copernicus holds a

special trophy in that it was the first crater around which secondary craters

were depicted (by Cassini in his map of 1680). Look carefully at Figure

8.13(b) and you will see many of the small craters and chains of small


Figure 8.13 (cont.)(d) Copernicus imaged byTerry Platt, using his318 mm tri-schiefspieglerreflector and StarlightXpress CCD camera (otherdetails not available).

(d)

craters surrounding Copernicus. These must have been produced by the

debris ejected explosively from the impact site during the crater’s forma-

tion. Figure 8.13(e) provides a wider-angle view. Imagine what it must have

been like in the region in the aftermath of that great explosion – blocks of

rock and other debris raining down as the seismic shock waves still

rumbled through the ground!

It is reckoned that Copernicus was created about 0.8 billion years ago,

the time from then to the present day now being known as the Copernican

era of lunar chronology. The Apollo 17 astronauts brought back rock

samples, including some which are taken to be part of the Copernican

8.13 COPERNICUS 195

Figure 8.13 (cont.)(e) Wider angle view of (b),showing the extensivepattern of secondarycraters which surroundCopernicus.

(e)

ejecta blanket. If these have been correctly identified then we can be even

more precise with our dating of Copernicus. Laboratory analysis of these

rocks suggest an age of 810 million years.

Large craters of similar ages as Copernicus, and younger, tend to have

bright interiors and possess ray systems. The ray system associated with

Copernicus is the second most prominent and extensive on the Moon.

While traces of the rays can be faintly seen at all but the lowest Sun

angles, the rays really only become very prominent around the time of full

Moon. Figure 8.13(f) shows a wide-angle view of the Copernican ray system


Figure 8.13 (cont.)(f) The ray systems ofCopernicus (just left ofcentre) and Kepler (to theright) show up well in thisnear full-phase photo-graph by Tony Pacey, takenon 1991 November 23d

using his 10-inch (254 mm)Newtonian reflector andeyepiece projection onIlford FP4 film. The brightfeature with a comet-liketail, below and a little tothe right of Kepler, isAristarchus.

(f)

under a high Sun. The photograph, obtained by Tony Pacey using his

254 mm reflector, shows that the interior of the crater is brighter than the

rays. These are wispy and plume-like, unlike the longer and straighter rays

of Tycho (the premier rayed crater, discussed in Section 8.46). The whole ray

system is very confused with many ray components not being exactly radial

to the centre of the crater. Some rays even meet the crater rim tangentially.

The confusion is compounded by the Copernican ray system merging with

the rays emanating from the crater Kepler to the west of Copernicus.

Figure 8.13(g) shows an Orbiter IV photograph of Copernicus with the

inner part of its ray system and the secondary craters in the quadrant to

the north-east of the crater.

8.13 COPERNICUS 197

Figure 8.13 (cont.)(g) Orbiter IV photograph ofCopernicus and its envi-rons to the north-east,showing the inner part ofthe ray system and theejecta pattern of sec-ondary craters. (CourtesyNASA and Professor E. A.Whitaker.)

(g)

8.14 CRISIUM, MARE [CENTRED AT 17°N, 59°E] (WITH CLEOMEDES,LICK, PEIRCE, PEIRCE B, PICARD, PROCLUS, YERKES)

Easily visible to the naked eye as a dark patch near the Moon’s north-east

limb, the Mare Crisium also tends to grab the attention of the telescope

user. This is especially the case when the terminator begins to cross it a

little after full Moon (see Figure 8.14(a)). In part, this is because it is com-

pletely detached from the main system of lunar maria. It is reckoned that

the Crisium Basin was formed about 3.9 billion years ago and the main

episode of lava flooding occurred a few hundred million years after that.


Figure 8.14 (a) Eveningfalls over the MareCrisium. Below the mare isthe prominent large craterCleomedes. Just to theright of the mare is thebrilliant small craterProclus, with itsasymmetric ray system.Photograph by Tony Pacey,taken using his 10-inch(254 mm) f/5.5 Newtonianreflector on 1992 January22d 00h 05m UT, when theSun’s selenographiccolongitude was 115°.7.The image was projectedby eyepiece to approxi-mately f/50 onto Ilford FP4film for this 0.5 secondexposure.

(a)

8.14 CRISIUM, MARE 199

Figure 8.14 (cont.)(b) The western section ofthe Mare Crisium. Samedetails as for Figure 8.1(see text, page 156). Thelargest crater on the mare,here on the left, is Picard.To the upper right ofPicard is the incompletering of the flooded craterLick (with a small, well-formed crater immediatelybelow it). The even lesscomplete Yerkes lies on theborder of the mare to theright of Picard. To thelower right of Picard arePeirce (the larger crater)and Peirce B. To the west ofthe mare (and to themiddle right on this pho-tograph) is the brilliantProclus, with its promi-nent and highly asymmet-ric ray system. (CatalinaObservatory photograph –courtesy Lunar andPlanetary Laboratory.)

(b)

The basaltic covering probably extends to about 1 km deep at the middle

of the mare, this being the deepest point of the Crisium Basin.

Though the Mare Crisium looks very elliptical and longest in the

north–south direction, the appearance is deceptive because of the fore-

shortening near the limb. Actually it is rather hexagonal (more than truly

elliptical) in outline – and it is extended in the east–west direction (570 km,


Figure 8.14 (cont.)(c) The northern to thewestern regions of theMare Crisium photo-graphed with the 1.9 mreflector of the HelwanObservatory at Kottamia on1965 August 1d 20h 39m UT(Sun’s selenographiccolongitude 311°.1). Lowerright of the mare is theprominent craterCleomedes. The ‘flyingeagle’ effect of Yerkes isparticularly apparent here.(Reproduced with the kindpermission of Dr T. W.Rackham.)(d) Peirce and Pierce Bdrawn by Roy Bridge.

(d)

against its north–south diameter of 450 km)! Clearly the impactor that

created the Crisium Basin hit the surface at a very low trajectory.

The south-eastern sector of the Mare Crisium is notable for the

Promontorium Agarum, and this is described in Section 8.1 (and shown

in Figure 8.1), earlier in this chapter. Figure 8.14(b), reproduced here,

shows much of the western half of the mare. The details are the same as

for the photograph in Figure 8.1 (see text, page 156). The northern half of

the Mare Crisium is well shown in Figure 8.14(c), which is a photograph

taken with the 1.9 m reflector of the Helwan Observatory at Kottamia in

Egypt.


Figure 8.14 (cont.)(e) Cleomedes is the largecrater near the bottom ofthis CCD image taken byGordon Rogers on 1996November 27d 23h 46m UT.He used his 16-inch(406 mm) Meade LX200telescope and StarlightXpress CCD camera. TheSun’s selenographiccolongitude was 107°.2.

(e)

Numerous odd appearances have been reported at various locations in

the mare, especially near the Promontorium Agarum (see Section 8.1).

These have usually been instances of apparent mistiness obscuring details.

However, local changes of albedo with Sun angle are probably the real

cause of these. It also used to be said that Mare Crisium shows a very strong

green tint to observers, more so than the other lunar seas. However, I have

never seen the greenish tint to be any stronger than elsewhere. In my

opinion the strongest mare colouration is that of Mare Tranquillitatis,

which often looks an inky blue to my gaze. Do let me repeat, though, that

the real colours of the Moon are various shades of brown. The observer’s

eye tends to normalise the overall colour as white, so producing the range

of apparent tints actually observed.

Various mottled patches, light spots and streaks abound on the mare

and some wrinkle ridges show up under the lowest angles of illumination.

The largest crater on the mare is the 23 km diameter Picard. It has a sharp

rim and a small central mound on the deepest part of its floor, which lies

about 2.4 km below the rim.

South-west of Picard, against the coastline of the mare, is the remnant

of an old flooded crater named Lick. Further along the shoreline, and to the

west of Picard, lays another broken partial ring, Yerkes. With the raised

ridge that joins the surviving wall of Yerkes to a small crater, the whole

forms an effect that has been aptly nicknamed ‘the flying eagle’. Figure

8.14(c) shows this appearance particularly well.

Going approximately northwards from Picard, Peirce is the next largest

of the well-formed craters on the Mare Crisium. It is almost as deep as

Picard, despite its much smaller diameter (19 km). Again of similar depth,

though even smaller, is Peirce B, just to the north of Peirce. On older maps

Peirce B is referred to as Graham, or sometimes Peirce A. The IAU-approved

designation is Peirce B. Peirce and Peirce B can look extremely dark under

early morning illumination, as is well shown in Figure 8.14(c). Compare

their appearance with the views shown in Figure 8.14(a) and (b). An impres-

sive drawing of their appearance under late evening illumination is shown

in Figure 8.14(d).

About 70 km west of the western shore of the Mare Crisium resides the

28 km diameter, but rather polygonal, crater Proclus. The early morning

view in Figure 8.14(c) shows its shape well. However, under a high Sun the

crater becomes one of the most brilliant on the Moon and its structure

is then much harder to make out; see Figure 8.14(b) for comparison. At

these times it also possesses a very bright system of rays, as can be

seen on Figures 8.14(a) and (b). The ray pattern is very asymmetric. Faint

rays do cross onto the Mare Crisium but mostly they extend towards

the north-west.


Proclus, and particularly its rays, often takes on a distinctly yellowish

colour but this is mainly due to spurious colour (the prismatic effect due

to the Earth’s atmosphere that often produces false colours along bright-

ness boundaries in the images of celestial bodies as seen through tele-

scopes).

Lunar north of the Mare Crisium (north-west as far as the orientation

as seen in a telescope goes) lies the magnificent crater Cleomedes. About

100 km of rough ground separates the peculiarly straight section of the

border of the mare from the rim of Cleomedes. Cleomedes is very deep.

The roughly terraced walls in places plunge more than 2.7 km down to

the convex floor of the crater. It contains several interior craters and

other features of interest to the telescope user. The crater is well shown

in Figure 8.14(c). Figure 8.14(e) shows it under the opposite lighting

effect.

8.15 ENDYMION [54°N, 57°E] (WITH ATLAS, ATLAS A, BELKOVICH,CHEVALLIER, HERCULES, MARE HUMBOLDTIANUM)

The limb regions of the Moon offer a challenge to the observer because all

details are distorted by foreshortening. The dimensions are only what

they seem to be along arcs concentric with the limb of the Moon.

Maximum contraction occurs along lines which are radial to the centre

of the Moon’s disk and the effect increases rapidly with proximity to the

limb.

To compound matters, librations often conspire to move formations

even closer to the limb just when the sky is clear and the lighting would be

suitable over the chosen formation for studying it. On the other hand,

librations can sometimes help by moving limb features further on to the

Moon’s Earth-facing side. One just has to make the best of the opportu-

nities that arise.

The crater Endymion serves as a fairly prominent marker to some

limb-hugging formations of particular interest. It is an old ring, 125 km

in diameter, with a rather smooth and dark floor, it having been flooded

with mare-type basalts. Endymion is shown at the centre of Figure 8.15(a).

Before its flooding the crater must have been quite deep. As it is, the walls

rise to over 4.5 km above the present flood-plain. Various spots and

streaks are visible on the crater floor but any surface relief (craters, etc.)

is very difficult for the backyard observer to detect. Figure 8.15(b) is a

superb CCD image of Endymion, by Gordon Rogers, in which the shadows

cast by the rugged peaks of the crater rim are seen thrown across the

crater floor.

A spectacular pairing of craters, Atlas and Hercules, lie to the south-

west of Endymion. They are well shown upper right in Figure 8.15(a) and


8.15 ENDYMION 205

Figure 8.15 (a) Endymionlies near the centre of thisCatalina Observatory pho-tograph. It was taken withthe 1.5 m reflector but Ican’t give the date, timeand exact colongitude(though I estimate this tobe about 38°) as the dataare not available. Thecraters Atlas and Herculesare to the upper right(with Atlas A andChevallier to their left).Part of the MareHumboldtianum can beseen near the lower leftand the crater Belkovichcan (with difficulty) beidentified in the lowermiddle of the frame.(Courtesy Lunar andPlanetary Laboratory.)

(a)

in the upper part of Figure 8.15(b). The larger of the two is Atlas, at 87 km

diameter. Its rim averages about 3 km in height above the deepest part of

the crater, near its centre. As is well shown in Figure 8.15(b), the floor is

very rough and hummocky and it has a ring of mountains at its centre,

rather than a central peak. Numerous fissures and small craters can be

seen under particularly good conditions if one is using a powerful tele-

scope.

Hercules is 69 km in diameter and it is obviously older than Atlas,

having walls which are clearly broken down to a greater degree. Various


Figure 8.15 (cont.)(b) Endymion (lower-rightcorner), Chevallier, Atlas A,Atlas and Hercules(extending from middleleft to upper right) areshown on this image madeby Gordon Rogers usinghis 16-inch (406 mm) MeadeLX200 telescope andStarlight Xpress CCD cameraon 1996 November28d 00h 50m UT, when theSun’s selenographiccolongitude was 107°.7.

(b)

landslips in the terraces also become evident when the lighting is correct

and I wonder how much of the damage we see today was caused by the

impact which gave rise to the nearby Atlas? The floor of Hercules is more

heavily covered with larger craters than that of Atlas, another indicator of

its greater age.

If you take a look at Figure 8.15(a) and project a line from the upper part

of the rim of Hercules, head it towards the upper part of Atlas and continue

it on for a distance roughly equal to the diameter of Atlas you will come to

a small but prominent well-formed crater. This is Atlas A, which is 22 km

8.15 ENDYMION 207

Figure 8.15 (cont.)(c) Belkovich and northernMare Humboldtianumdrawn by Roy Bridge.

(c)

in diameter. Immediately to the left of Atlas A is a ‘ghost ring’ crater – one

that has been flooded almost up to its rim. This is the 52 km diameter

Chevallier. Note the small crater within Chevallier, obviously post-dating

the episode of flooding.

In fact, it probably strikes you that this is an area of the Moon which

shows extensive evidence of mare-type flooding. This characteristic is very

evident in Figure 8.15(b). Yet this area in not actually on a lunar sea. The

Mare Frigoris and Lacus Mortis are nearby, though, and the demarcation

between lunar maria and lunar terrae is here rather less definite than in

most other places.

The extreme limb features, first referred to, are the Mare Humboldtianum

and the crater Belkovich. Mare Humboldtianum was named by Mädler,

with a sense of appropriateness, after the German explorer Alexander von

Humboldt. Humboldt’s discoveries spanned, and you could say linked, the

eastern and western hemispheres of the Earth.

Mare Humboldtianum is one of the smaller of the lunar ‘seas’. Its

diameter averages about 260 km but its shape is decidedly irregular

when seen in plan view. Belkovich attaches to it on the north-western

side. It is an old crater (of what used to be called the ‘walled plain’

variety), 198 km diameter, with two large craters intruding into its walls

on the west and a further flooded ring on the eastern flank (and span-

ning the connection to the mare). The northern part of the mare is

shown on the lower left of Figure 8.15(a) and Belkovich can be made out

almost attaching to the mare’s northernmost section. Neither are

well shown, despite the very favourable libration when this Catalina

Observatory photograph was taken. Roy Bridge has made a valiant effort

to draw these features and the result is shown in Figure 8.15(c). If you

relish a challenge, you might like to try recording this very difficult area

yourself.

8.16 FRA MAURO [6°S, 343°E] (WITH BONPLAND, GUERICKE, PARRY)This area of the Moon lies a little beyond the north-west border of the

Oceanus Procellarum and on older maps occupied part of the Mare

Nubium. However in 1964, after the successful flight of Ranger 7, the area

was re-named Mare Cognitum (the Known Sea). Ranger 7 transmitted the

first close-range photographs of a lunar mare before it was deliberately

crashed in this section of the mare. Officially the Mare Cognitum extends

out to an average radius of 170 km centred on a position 10°S, 337°E.

Several spacecraft have either been deliberately crashed or have soft-

landed in this area. In particular, the Apollo 14 astronauts Alan Shepard and

Ed Mitchell landed in the foothills less than 30 km to the north of the

northern rim of the great crater Fra Mauro (see Chapter 6 for more details).


209

Figure 8.16 (a) Fra Maurois the largest crater in thelower right section of thisCatalina Observatory pho-tograph, taken on 1966May 29d 03h 51m UT (at acolongitude of 22°.2) withthe 1.5 m reflector. Thetwo craters attached to theupper part of Fra Mauroare Parry (on the left) andBonpland. The largestcrater in the upper-leftsection of this photographis Guericke. (CourtesyLunar and PlanetaryLaboratory.)

(a)

Whenever I look at the area north of Fra Mauro through a telescope I can

never help but imagine them scuttling about ‘down there’, wheeling their

Modular Equipment Transporter (‘handcart’, to you and me) all those years

ago.

The Imbrium ejecta blanket is very evident in this region of the Moon

and the patterns of ridges and scarring, radial to the Imbrium Basin, are


Figure 8.16 (cont.)(b) Parry and Bonpland,drawn by Nigel Longshaw.Necessarily being reducedin size for reproduction inthis book, some of thehand-written notes are toosmall to read easily. Theblock of descriptive textreads (with no editing byme): The rille or cleft runningfrom the N/E wall of Parrydoes not appear on somecharts and is shown onWilkins’ map as a craterchain. The craterlet at thenorthern tip of this rille waselongated in shape with alight ‘patch’ to its northernsurrounds. The rille runningN/S through Bonpland waswell defined although seemedto be affected by a lightershaded area on the innersouth wall of Bonpland,making the rille difficult todistinguish at this point.Several small white patches inthe area correspond to crater-let positions.

(b)

obvious even through small telescopes. Spacecraft results show this area to

be very rich in KREEP (see Chapter 6), being one of the main ‘hot spots’ in

gamma-ray maps.

Fra Mauro, itself, is 95 km in diameter. As can be seen from Figure

8.16(a), it is an old, ruined and flooded, ‘ring-plain’. A section of the wall to

the east is completely missing. The floor is extensively cratered and ridged,

8.16 FRA MAURO 211

Figure 8.16 (cont.)(c) Parry, drawn by NigelLongshaw.

(c)


Figure 8.16 (cont.)(d) Guericke, drawn byNigel Longshaw. The blockof descriptive text reads:An attempt to recover theappearance of a ‘valley’ to theN. of M and E. of outer ram-parts of Parry as observed byH. Hill on 1996.2.27 (and pos-sibly Elger from his desc.).Seeing was far from good andI was restricted to �160 (alsotwilight sky). However, I wasstruck by the alignment ofridges in the area in question,perhaps the unresolved iso-lated peaks noted by the twoobservers?

(d)

mostly in the roughly north–south direction in common with the radial

ejecta pattern from the Imbrium Basin. Another two ‘ring-plain’ craters

attach to Fra Mauro: Bonpland and Parry.

Bonpland is the larger of the two, at 60 km diameter, and shares its rim

with that of Fra Mauro along the southern section of the latter. Although

Bonpland superficially looks older (more degraded) than Fra Mauro, a close

examination of the shape of the augmented rim at the intersection, sug-

gests the opposite. In turn both Fra Mauro and Bonpland have been

intruded upon by the still younger Parry. Parry is 48 km in diameter. The

grouping is well shown in Figure 8.16(a) and in the special studies by Nigel

Longshaw in Figures 8.16(b) and 8.16(c).

To the south-south-east of the ‘Fra Mauro trio’, and separated from

them by about 100 km of very interesting terrain, is another ancient relic

of a crater: Guericke. It has a diameter of 64 km. It, too, is well shown in

Figure 8.16(a). Figure 8.16(d) is another of Nigel Longshaw’s splendid draw-

ings.

Rather than me providing all the intricate details of this very interest-

ing area of the Moon, I thought I would leave this as a project for you. With

the features generated by the Imbrium Basin event 3.85 billion years ago as

a ‘time marker’, you might like to have a go at ‘untying the temporal knot’

and reconstruct the sequence of events which generated the features we

see today.

The Fra Mauro region of the Moon may not be the most attention grab-

bing when one is looking through the telescope eyepiece but it more than

makes up for that if one is prepared to really study the small details.

8.17 FURNERIUS [36°S, 60°E] (WITH FRAUNHOFER, FURNERIUS B,FURNERIUS J, PETAVIUS)

Furnerius is the southernmost member of what used to be called “the great

western chain of craters”. This was before the IAU reversed east and west

on the Moon, so we might now call the arrangement ‘the great eastern

chain’. All lying on virtually the same meridian, the ‘chain’ comprises the

craters Furnerius, Petavius, Vendelinus and Langrenus, with the Mare

Crisium also included and the crater Endymion to the north of the Mare

Crisium (Cleomedes is a little further from the shared meridian than the

other members). This ‘chain’ was used as evidence that craters were distrib-

uted in definite patterns, rather than randomly, and so must be of endo-

genic rather than impact origin.

The evidence for the impact scenario is so overwhelming that it surely

must be the correct one (though a few individuals still support the endo-

genic scheme). However, ‘the great eastern chain’, as I propose to call it,

8.17 FURNERIUS 213

certainly makes one pause for thought when the ambient lighting throws

it into prominence (see Figures 8.17(a) and (b)). It really does seem, though,

to be a coincidence. Certainly the members of the ‘chain’ are all of differ-

ent ages.

Of the other ‘chain’ members, Vendelinus and Langrenus are discussed

in Section 8.26 further on in this chapter, while the Mare Crisium is dis-

cussed in Section 8.14 and Endymion in Section 8.15, earlier in this chapter.

The 125 km diameter Furnerius is obviously very old, as witness its some-

what degraded appearance and the number of large craters strewn over its

interior. The crater walls climb to about 3.5 km above the level of its interior.

Figure 8.17(c) is a magnificent drawing of this feature by Nigel Longshaw. The


Figure 8.17 (a) The twoprominent craters, largelyfilled with black shadow,on the Moon’s terminatorare Furnerius (upper) andPetavius (lower, withcentral mountain pokingup into the sunlight).Photograph by Tony Pacey.He used his 10-inch(254 mm) Newtonianreflector, with eyepieceprojection to obtain thisview on 1991 November23d. Others details notavailable.

(a)

largest crater in the interior of Furnerius is Furnerius B. This 22 km diame-

ter crater is situated near the western rim of Furnerius. The slightly larger

(24 km) crater that spans the north-east rim is Furnerius J. The floor of

Furnerius abounds in interesting details, including the prominent rille that

snakes from the north-west wall through the centre of the crater.

One month earlier, Nigel Longshaw observed Furnerius at a slightly

later colongitude. His drawing is shown in Figure 8.17(d). The crater to the

8.17 FURNERIUS 215

Figure 8.17 (cont.)(b) Furnerius (uppercrater), Petavius (middle)and Vendelinus (lower)photographed by TonyPacey on 1989 October 16d,same details as for (a).

(b)

south of Furnerius, and almost attached to it, is the 57 km diameter

Fraunhofer. Sequence drawings of the Sun rising and/or setting over a

lunar feature are particularly instructive as the detailed height relation-

ships are then revealed. Note which parts of Furnerius are last to sink into

the darkness of lunar night on Nigel’s drawing. An Orbiter IV photograph of

Furnerius is presented in Figure 8.17(e).


Figure 8.17 (cont.)(c) Furnerius, drawn byNigel Longshaw. The blockof descriptive text reads(with no editing by me):Excellent chance for furtherwork on this feature: seeingstarted quite poor so lowerpowers were used to block inthe main details. Conditionsimproved rapidly, and awealth of detail was visibleeven at �200. It becameobvious there was far toomuch to deal with in onesession, but as much as practi-cal was recorded. The easternwall was very complex and isnot depicted in any greatdetail, although I found the‘clefts’ running down to thecrater floor particularly inter-esting. The shadow cast by theE. wall was deformed by fea-tures to the east. Brightestpart of the wall was to thesouth where a ‘valley’ runsdown to the crater floor. Thewhole southern floor was verycomplex and details ‘popped’in and out during the bettermoments. The crater group tothe centre west of the southernfloor was particularly detailedwith a bright ‘spot’ to itsimmediate S. W. RimaFurnerius was well observedalong with several other ‘rillelike’ features scattered overthe surface.

(c)

North of Furnerius, the crater Petavius must rank as one of the most

beautifully sculpted objects on the Moon. It is the centre one of the ‘chain’

of craters shown in Figure 8.17(b). The outer walls of this great ‘dinner

plate’ of a crater span 177 km but notice the unusually wide inner terraces,

even tending to a double-ring type of structure along the western periph-

ery. The inner ramparts extend upwards to approximately 2.1 to 3.3 km

above the floor, the height varying around the crater.

8.17 FURNERIUS 217

Figure 8.17 (cont.)(d) Sunset over Furnerius,drawn by Nigel Longshaw.The block of descriptivetext reads: Seeing conditionsrather poor at commence-ment, but as Moon rose seeingimproved greatly. A wealth ofdetail was visible along theeastern wall of Furnerius,during the steady momentstoo much to depict. It wasinteresting to follow theretreat of the visible surface tothe southern floor and details1 and 2 to the right depict the‘shrinking’ of this feature(extent shown on maindrawing detailed at com-mencement of sketch.)

(d)


Figure 8.17 (cont.)(e) Orbiter IV photograph ofFurnerius. (Courtesy NASAand Professor E. A.Whitaker.)(f) Petavius. CCD image byTerry Platt, obtained usinghis 318 mm tri-schief-spiegler reflector andStarlight Xpress CCDcamera. No other detailsavailable. The author hasapplied slight image sharp-ening and brightness andcontrast re-scaling.

(e)

(f)

The mighty central mountain complex soars up to 1.7 km above the

crater floor but is raised another 0.5 km, or so, above the level at the periph-

ery because the crater floor is highly convex.

It is fascinating to watch the progression of shadows when Petavius is

close to the terminator. The area around the central mountains, and then

the central mountains themselves, are always last to disappear at sunset

and first to appear at dawn, with the rest of the interior of the crater largely

filled with deep-black shadow at these times. Something of the effect is

shown in Figure 8.17(a).

Figure 8.17(f) shows one of Terry Platt’s incredible CCD images. The

fineness of the detail shown is readily apparent by considering that only

part of the formation fits into the frame!

The convexity of the floor gives a clue to the origin of one of the most

outstanding of Petavius’s features: the remarkable fissure that crosses the

floor from the central mountains to the south-west wall. This used to be

called “the Great Cleft of Petavius” but the term ‘cleft’ is now obsolete. I

suppose that it should now be known as ‘the Great Rille of Petavius’. It

seems to be a graben, a deep-seated stress fracture caused when the

ground is pulled apart to either side and the ground along it slumps down-

wards into the crack. Other rilles are visible, mostly at least approximately

radial to the central mountains. However, these are all very much harder

to see than ‘the Great Rille’. When the Sun-angle is low over the area ‘the

Great Rille’ is easy to see even through a 60 mm refractor. Of course when

the Sun is high it becomes a difficult object to view even through a large

telescope.

As I said, the convexity of the floor provides the clue to its formation. It

seems that enormous forces have built up under the floor of the crater,

raising its floor and causing the stress fractures. As to the cause of the

forces . . . .

8.18 ‘GRUITHUISEN’S LUNAR CITY’ [5°N, 352°E]Baron Franz von Gruithuisen was born in Bavaria in 1774. He took a

medical degree but turned to astronomy as a profession, becoming

Professor of Astronomy at Munich in 1826. He was an energetic selenogra-

pher and generally a good observer. However he did tend to bring ridicule

upon himself by making some extraordinary claims – the fruits of a vivid

imagination.

Most famously, in 1824 he announced his “discovery of many distinct

traces of lunar inhabitants, especially of one of their colossal buildings”.

He further described “a lunar city” with “dark gigantic ramparts”. The site

of this edifice is quite near the centre of the Moon’s disk, less than a

hundred kilometres north of the ruined 35 km diameter crater Schröter.

8.18 ‘GRUITHUISEN’S LUNAR CITY’ 219

Actually, the southern point of the “lunar city” is the 10 km crater

Schröter W.

Of course, there is nothing but a rough arrangement of hills to be seen

in that location. Figures 8.18(a) and 8.18(b) show two splendid studies of

Gruithuisen’s fabled ‘city’ made by Andrew Johnson.

Not everything one does at the eyepiece of the telescope has to be for

serious study. Just for the fun of it you might like to take a look at the area

yourself, particularly around the times of first and last quarter Moon, and


Figure 8.18 (a) What a pitythere are no selenitesbusying themselves in themorning within theconfines of the ‘lunar city’,as Gruithuisen had inter-preted this structure!Drawing by AndrewJohnson.

(a)

see if you can force your imagination to create a lunar city out of the

jumbled topographic features in the area just north of Schröter.

Before we laugh too loudly at the memory of Gruithuisen, we should

remember that he made many good contributions to the study of the

Moon in his day and has been commemorated with a 15 km crater named

after him positioned at 33°N, 320°E on the lunar surface, at the junc-

tion of the Mare Imbrium and Oceanus Procellarum. He can even be said

to be the originator of the impact theory of the formation of lunar

8.18 ‘GRUITHUISEN’S LUNAR CITY’ 221

Figure 8.18 (cont.)(b) Gruithuisen’s ‘lunarcity’ in the late afternoon,as drawn by AndrewJohnson.

(b)

craters – after many years of dispute among experts, now the accepted

scenario!

8.19 HARBINGER, MONTES [27°N, 319°E] (WITH PRINZ)The Harbinger Mountains, more properly Montes Harbinger, are a small

but interesting cluster of hills situated in a fairly barren part of the

Oceanus Procellarum just a little north-east of the prominent crater

Aristarchus (see Section 8.7). The proximity of Aristarchus is evident in

Figure 8.19(a), which is a Catalina Observatory (1.5 m reflector) photograph

taken on 1965 December 6d 05h 14m UT, when the Sun’s selenographic

colongitude was 63°.7. You might find this view useful in helping to locate

the mountain group through the telescope eyepiece.

The individual peaks are like islands rising up from the Ocean of

Storms. A ruined crater, Prinz, attaches to the south-west of the range.

Prinz forms an incomplete ring with a diameter of 47 km. Clearly the

Procellarum lavas have partially buried this crater, along with the lower

parts of the Harbinger Mountains and doubtless other low-lying features.

Prinz is completely open to its south-west.

Numerous rilles and even some domes (volcanic swellings) are evident

in the area and become evident at different stages of illumination. Figure

8.19(b) is a drawing by Roy Bridge showing the group under the first light


Figure 8.19 (a) MontesHarbinger is at the centreof this photograph, withthe incomplete craterPrinz abutting the moun-tain group to the upperright. The crater at the top-right corner of thisCatalina Observatory pho-tograph is Aristarchus.(Courtesy Lunar andPlanetary Laboratory.)

(a)

of lunar dawn. Figure 8.19(c) shows the area under a much higher Sun.

Figure 8.19(a) shows it under a slightly higher Sun-angle, still.

I would unhesitatingly recommend the aspiring draughtsman of the

lunar scene to gain practice at drawing mountains by observing and

recording the Harbinger–Prinz complex under as many different illumi-

nations as possible. The details are delicate enough to make it a real

challenge but not so overwhelmingly complex as to be off-putting. After-

all, even the most practised observer–draughtsman would balk at the

8.19 HARBINGER, MONTES 223

Figure 8.19 (cont.)(b) Sunrise over MontesHarbinger, drawn by RoyBridge.

(b)


Figure 8.19 (cont.)(c) Prinz and MontesHarbinger, drawn byAndrew Johnson.

(c)

prospect of trying to record even part of extensive ranges, such as Montes

Apenninus!

8.20 HEVELIUS [2°N, 293°E] (WITH CAVALERIUS, GRIMALDI,LOHRMANN)

The impression of the apparent non-accidental alignments of some craters

on the Moon is, at least in part, generated by the presence of the termina-

tor. How many prominent chains of large craters can you find that extend

in even a roughly east–west direction? Yet time and time again crater

chains along the north–south meridians spring into prominence as the

morning and evening terminator looms close. Such an example is provided

by the craters Grimaldi, the southernmost member, and extending north-

wards, Lohrmann, Hevelius and Cavalerius. Seen just before full Moon this

line of large craters appears strikingly prominent even in the smallest tele-

scope.

Figure 8.20(a) shows a ‘snapshot’ of the spectacle I took myself. Figure

8.20(b) is another example, though this time with the terminator slightly

less advanced and the largest crater (Grimaldi) here entirely filled with

shadow and forming a distinct ‘notch’ in the Moon. This ‘notch’ is obvious

even when seen through low-power binoculars.

8.20 HEVELIUS 225

Figure 8.20 (a) The line ofcraters Grimaldi toCavalerius is very apparentalong the terminator inthis photograph taken bythe author on 1983October 19d, using his0.46 m Newtonianreflector. The camera,fitted with a 58 mm lens,was hand-held to a 44 mmPlössyl eyepiece (EFR�f/7.4) for a 1/500second exposure onEktachrome 200.

(a)

Figure 8.20(c) shows a detailed study of Hevelius, together with

Lohrmann and Cavalerius, made by Andrew Johnson. Hevelius is a magnifi-

cent crater, 120 km in diameter, with some terracing and much fine detail

visible in its somewhat irregular walls. It can be said to represent an

example of a formation intermediate in type between the ‘saucer-shaped’

and ‘walled-plain’ craters. It is, though, rather closer to being of the

‘walled-plain’ variety than the other.

The floor is convex as is evident in Figure 8.20(b). The walls vary in

height around the crater but typically soar up to about 1.8 km above the

floor. The crater has a central mountain, as well as other floor details such

as rilles and small craters. Hevelius is named after Johann Hewelcke, a

seventeenth century Danzig astronomer and selenographer, and the crater

is called “Hevel” on old maps.

Lohrmann is a 34 km diameter crater which seems to sit uneasily

between Hevelius and Grimaldi. It has a rather hummocky floor and a

central mound.


Figure 8.20 (cont.)(b) Grimaldi is entirelyshadow-filled, creating a‘notch’ in the Moon, whileLohrmann, Hevelius, andCavalerius are prominentlydisplayed below Grimaldion this photograph takenby the author using his0.46 m reflector on 1985January 5d 20h 23m UT(when the Sun’s seleno-graphic colongitude was67°.8). The camera, fittedwith a 58 mm lens, washand-held to a 9 mmOrthoscopic eyepiece (EFR�f/36) for the 1/125 secondexposure on Fuji HR1600film.

(b)

8.20 HEVELIUS 227

North of Hevelius, and just intruding into it, is the 64 km diameter

Cavalerius. That Cavalerius is more youthful than Hevelius is evident both

in its crisper appearance and in the fact that it is obviously Cavalerius which

has intruded across the rim of Hevelius and not the other way round.

There is, though, some slumping of the rims of both at their intersec-

tion. In the case of Cavalerius the slumping is slight. In the case of

Figure 8.20 (cont.)(c) Hevelius (largestcrater), Lohrmann (aboveHevelius) and Cavalerius,drawn by Andrew Johnson.

(c)


Figure 8.20 (cont.)(d) Hevelius, withLohrmann and Cavalerius,drawn by Andrew Johnson.Note the differences to thedrawing in (c), largely theresult of the differentlibration.

(d)

8.20 HEVELIUS 229

Hevelius it is considerable. Also the ground outside Hevelius in which

Cavalerius was formed is lower, anyway, that the rim of Hevelius. This

creates the illusion of a deep channel apparently joining Hevelius to

Cavalerius when the formations are close to the terminator. Even the low-

resolution view of the arrangement in Figure 8.20(b) shows this effect

well. The exaggerated effect persists to quite a high Sun-angle because the

rim of Hevelius just east of the point of intersection casts a long shadow

down into Cavalerius.

Similar is the so-called ‘Miyamori Valley’. This is an apparent chasm

extending from Lohrmann south-westwards to the major crater Riccioli.

Again it is an exaggerated effect for the most part generated by the

shadows cast by the rather linear NNE section of the outer ramparts of

Grimaldi. Any real valley is much less deep and well defined, being at most

some low ground that threads between assorted hummocks and craters.

Figure 8.20(e) shows a study of it by Roy Bridge. Notice how the shadow

fades away, like the grin of a Cheshire cat, at the eastern end of the ‘valley’

as the terminator moves westwards. This sort of sequence drawing is

highly instructive.

Figure 8.20(f) shows the area under higher Sun. The ‘valley’ has all but

Figure 8.20 (cont.)(e) The ‘Miyamori Valley’,drawn by Roy Bridge.

(e)

disappeared. However, some arcuate rilles are now in evidence curving

westwards away from Hevelius.

Being so close to the western limb of the Moon, the appearance of the

formations can alter quite significantly because of the effect of libration

in longitude. Compare Figure 8.20(c) with Figure 8.20(d), which is another

drawing by Andrew Johnson. Here the values of the Sun’s selenographic

colongitude are very similar and yet there are significant differences in

the way Andrew has represented the features – in large part caused by the

difference in the librations.


Figure 8.20 (cont.)(f) Portrait of Hevelius,Cavalerius and Lohrmann,made using the 1.5 mreflector of the CatalinaObservatory on 1966February 4d 06h 53m UT,when the Sun’s seleno-graphic colongitude was74°.2. (Courtesy Lunar andPlanetary Laboratory.)

(f)

8.20 HEVELIUS 231

Figure 8.20 (cont.)(g) Grimaldi (centre) domi-nates this CatalinaObservatory photograph,taken just 10 minutes afterthe one shown in (f).(Courtesy Lunar andPlanetary Laboratory.)

(g)

South of Lohrmann, and with a tract of rough and cratered ground sep-

arating the two, is the great ‘walled-plain’ Grimaldi. Completely in shadow

in Figure 8.20(b), the floor of this crater is just beginning to receive the rays

of the rising Sun in Figure 8.20(a). Figure 8.20(g) shows the formation

(together with Lohrmann and the southern part of Hevelius) in full sun-

light.

That Grimaldi is much larger than Hevelius is very obvious. However,

the exact size of Grimaldi is a little problematical. The very dark, lava-

flooded, floor of the formation is roughly 140 km in diameter but, as can

be seen from the photographs, is rather irregular in outline. Look carefully

and you will see that the rough surrounds of the flood-plain climb upwards

and form a vague crater rim (more obvious to the north and west) of diam-

eter exceeding 220 km. There are even, in places on the Moon, faint traces

of a secondary concentric ring at nearly twice the radius of the first. Clearly

the impactor that created Grimaldi packed quite a wallop!

Occasional bright flashes and patches of colour and apparent mistiness

have been reported from time to time on Grimaldi’s lava-flooded floor and

many small craters, mounds, spots, streaks and wrinkle ridges provide an

endless source of study for the telescopist.

8.21 HORTENSIUS [6°N, 332°E] (WITH ASSOCIATED LUNAR DOMES)Hortensius is a fairly unremarkable crater, 15 km in diameter, situated in

the Oceanus Procellarum just west of the great crater Copernicus. It has a

sharp rim and is quite deep for its size. Rim to lowest point in the bowl-

shaped depression measures nearly 2.9 km. The real point of interest lies

on the mare just to the north of the crater: several of the raised mounds

known as lunar domes.

Most casual observers of the Moon never get to see lunar domes. They

are invariably small and elusive, only showing up well at low Sun-angles.

Small-scale maps, and even some of larger sizes, do not show the location

of these intriguing formations. The domes near Hortensius are notable in

that their location is easily defined. Also they are at their most evident

close to the time of first quarter Moon, the most popular time for lunar

observing (they are again evident at last quarter Moon, of course, but far

fewer amateurs are out with their telescopes in the small hours of the

morning to observe the Moon).

As far as advice about locating the domes goes, I can do no better than

to refer you to Figure 8.21. On it you will see part of Copernicus to the far

left of the photograph, and so can gauge the scale. Upper right you will see

Hortensius and just below Hortensius you should be able to make out a

cluster of blister-like mounds. They are the lunar domes.


8.21 HORTENSIUS 233

Figure 8.21 The subject ofthis photograph,Hortensius and its associ-ated lunar domes, hasbeen placed near theupper-right corner inorder to show their loca-tion with respect to thenearby major craterCopernicus (partly shownon the left). Photographtaken with the 1.5 mreflector of the CatalinaObservatory on 1967January 21d 02h 44m UT,when the Sun’s seleno-graphic colongitude was31°.4. (Courtesy Lunar andPlanetary Laboratory.)

Historically, the proponents of the endogenic origin theory of lunar

craters used the domes to support their views. The domes, to them, were

blisters that had failed to burst (on the mud-bubble theory of crater forma-

tion) and so were examples of the crater-formation process ‘caught in the

act’. We can dismiss this theory in the light of modern evidence but the

question still remains: what are they and how do they fit into the scheme

of things lunar? Here opinions vary.

As is so often the case about features and processes on the Moon, various

authorities tend to give the impression that things are very ‘cut-and-dried’

and they usually give very definite explanations. The trouble is, you then

read what another authority says on the same subject, presented with equal

certainty, and yet differing from the explanation of the first one!

Some experts say that lunar domes are just mountains. Others, prob-

ably the majority, say that domes are volcanic swellings of the crust caused

by a magma build-up from below. Others compare them to earthly cinder-

cones and say they are true volcanoes.

I tend to side with the opinion that they are true volcanoes, though I

don’t agree with the cinder-cone interpretation. Many of them have what

appear to be calderas situated at their summits. In fact, most of the

Hortensius domes have summit craters; I think too many for chance

impacts to be responsible. I cannot help wondering about the outpouring

of low-viscosity lavas that flooded the great lunar basins. In particular, I

wonder about the sites of the eruptions. There is strong evidence that the

major lava flows originated from long fissures near the peripheries of the

basins. However could there have been other vents further in? It is certain

that the lavas did not switch off suddenly. Evidence for successive lava

flows abound on the lunar maria. The vents which ceased eruption early

were undoubtedly ‘levelled over’ with mare lavas but what of those that

were last to finish? Maybe the last vestiges of volcanism brought to the

surface rather less-fluid lavas – viscous enough to build up some vertical

structure around the caldera? Certainly the impact melts that would have

pooled inside the basins might provide the source of higher-viscosity

lavas.

If you will indulge me while I build on my speculations, perhaps the

domes have some connection with the newly formed mare striving to

achieve isostatic equilibrium. This is the theoretically expected process of

slight sinking of the layers of mare basalts after solidification. The cause

for this is the higher density of the basalt compared to that of the

bedrock. There is some evidence that this isostatic levelling process actu-

ally occurred on the Moon, in the form of faulting and apparent tide-

marks at the basin boundaries, etc. As the solidified ‘seas’ sank they

inevitably squeezed down on the layers below. Perhaps the domes

resulted as a little of the more viscous sub-mare lavas escaped through

fissures?

I must emphasise that this idea is not the slightest bit ‘official’. It is

merely the result of my musings and may be completely wide of reality –

as indeed may be many of the current ‘official’ ideas on the subject. If only

one thing can be taken as certain, it is that everybody cannot be right!

A lot of questions, with no universally agreed answers. Are the domes

really primarily up-lift features but with internal fissures creating lava

vents that open out at the peak in many cases? Maybe they instead

represent the last vestiges of the ancient lunar volcanism? I wonder.

I expect the definitive answer will have to wait until lunarnaut geologists

conduct seismic sounding experiments (setting off small percussive

charges and monitoring the resultant shock waves) at dome sites in

future decades.

The lunar domes are as interesting as they are a challenge to observe.


There are many more examples elsewhere on the Moon, a number of

them in the same general area as Hortensius. You will find domes very

hard to see in all but the lowest angles of illumination. Also they are a test

for good optics and good observing conditions. Image contrast is of prime

importance. If you observe with a large-aperture reflector, perhaps one of

the popular ‘Dobsonian’ telescopes, and can’t detect domes when you

think they should be visible, you might like to try masking the aperture

with an off-axis hole. Despite the reduction in light-grasp you might find

that the increase in contrast is enough to reveal the domes you could not

see before. This technique is especially useful if the atmospheric condi-

tions and/or the telescope optics are of indifferent quality. Happy dome

hunting!

8.22 HUMORUM, MARE [CENTRED AT 24°S, 321°E] (WITH

DOPPLEMAYER, GASSENDI, GASSENDI A, VITELLO)Mare Humorum (Sea of Moisture – a rather inappropriate name, that!)

might be one of the smaller of the lunar ‘seas’, its diameter averaging

400 km, but I think that it is certainly one of the most interesting. It is pic-

tured in Figure 8.22(a), a photograph taken by the 1.5 m reflector of the

Catalina Observatory on 1967 February 22d 03h 35m UT, when the Sun’s

selenographic colongitude was 61°.

The mare basalts fill the very ancient basin. In fact the Humorum Basin

is probably one of the earliest of them, at nearly 4.2 billion years old. This

is evident by the total absence of any identifiable ejecta pattern, obliterated

by the subsequent impacts and other events which have moulded the lunar

surface.

By contrast, the surface of the mare appears to be one of the youngest

of the great ‘seas’. This is implied by the crater-record and is consistent with

the results gained by the Apollo missions concerning the relative youthful-

ness of the westernmost of the lunar mare flood-plains. It is probable

that the final significant eruptions of mare basalts that covered the

Humorum Basin occurred not much more than 3 billion years ago. So,

Mare Humorum is both one of the oldest and one of the youngest of the

Moon’s great ‘seas’, depending on whether we are talking about the basin

or the lava flood-plain!

You might be wondering how the age of the mare can be gauged from

the craters on it. To understand that, remember how the meteoritic bom-

bardment of the Moon was severe early in its life and dwindled, both in

the sizes of the impactors and the frequency of impacts, with time. From

widespread studies of the numbers and sizes of craters on the Moon,

taken together with certain well-established age benchmarks obtained by

8.22 HUMORUM, MARE 235

laboratory measurements of lunar samples brought to Earth, planetolo-

gists are in a position to gauge the age of a given surface on the Moon.

Crudely put, if a given area of surface contains lots of large craters then

it is old. If a greater fraction of the area is weighted to smaller craters then

it is young. By making painstaking counts of craters and measurements

of their sizes scientists can quite reliably determine the age of particular

surfaces, such as the maria, on the Moon.

I find it difficult to believe that the Humorum Basin, along with the

other western basins, remained completely ‘dry’ while the basins on the

Moon’s eastern hemisphere were busily filling with basaltic lavas; the site

of the action only to switch to the Moon’s western hemisphere when things


Figure 8.22 (a) MareHumorum. The largestcrater (at the bottom ofthe photograph) isGassendi. Details in text.(Courtesy Lunar andPlanetary Laboratory.)

(a)

had quietened down in the east. I think it much more likely that the lava

flooding started in the west at more or less the same time as in the east.

However, I think that it continued for longer in the west.

If that is the correct scenario then certain consequences must follow.

For one thing, the basalt lavas of the western ‘seas’ must have a greater ten-

dency to overflow the basin rims (given the finite depth of the basins) and

spread over a much greater area of the Moon’s surface. Look at any photo-

graph of the full Moon and you will see that is indeed the case. Not only is

a much greater area of the Moon’s surface covered by dark mare material

but the edges of the lunar seas are much less well defined by their parent

basin rims.


Figure 8.22 (cont.)(b) A low Sun-angle overthe Mare Humorumreveals low-relief featuressuch as the wrinkle ridgeson the mare and thegraben on the junctionbetween it and the PalusEpidemiarum (towards theupper left). Details in text.(Courtesy Lunar andPlanetary Laboratory.)

(b)

The westernmost half of the Mare Imbrium spills into the Oceanus

Procellarum, which itself merges with the Mare Cognitum and Mare

Nubium. Even the Humorum Basin wall is breached to the north-east and

here the Mare Humorum spills into the Mare Nubium, and again to the

south-east where the flood-plain extends into the Palus Epidemiarum

(the ill-defined mare area south of the Mare Nubium), which itself

curves round the area outside the south-western periphery of the Mare

Humorum.

I would conjecture that future lunarnaut surveyors will find that the

western seas are composed of a number of sheet-like strata, and will find

fewer strata and generally thinner coverings to the basins in the east of the

Moon.

As far as an answer goes as to why the crust should be thinner to the

west of the Earth-facing meridian, well, maybe it has to do with the

“Gargantuan Impact” originally proposed by Dr Peter Cadogan. On his

theory the Oceanus Procellarum is really the lava in-fill of a 2400 km diam-

eter basin that resulted from a colossal impact in Pre-Nectarian times.

Here, though, I cannot claim to be on anything but thin ground, if you will

excuse the pun!

As has already been said, there is a paucity of large craters actually on

the Mare Humorum but there are some beautiful examples of craters situ-


Figure 8.22 (cont.)(c) Southern section of the‘shore’ of the MareHumorum. The well-formed crater on the leftof the group is Vitello. Tothe lower right of Vitello isthe largest crater of thegroup, Dopplemayer.Details in text. (CourtesyLunar and PlanetaryLaboratory.)

(c)

ated around the periphery of the mare that post-date the creation of the

basin and yet pre-date the lava flooding.

Again, this provides proof of a substantial interval between the two

episodes. If you doubt this, then consider how these craters could survive

the event that created the basin. They couldn’t. The craters must have

been formed after the basin. Then take a close look at the craters and you


Figure 8.22 (cont.)(d) Vitello, drawn byAndrew Johnson.

(d)

will see that in many cases the mare basalt has intruded into them, typi-

cally breaching the walls that face in to the mare, and partially flooding

their interiors. Obviously the flooding came after the craters were formed

– and hence the interval between the basin creation and the flooding

with mare basalts.


Figure 8.22 (cont.)(e) Sunset over Gassendi,drawn by Nigel Longshaw.

(e)

As always, a low Sun-angle reveals details of small vertical relief.

Figure 8.22(b) is another photograph taken with the 1.5 m Catalina

Observatory telescope, this time on 1966 December 23d 04h 54m UT

when the Sun’s selenographic colongitude was 39°.9 and the terminator

bisected the Mare Humorum. Several roughly concentric wrinkle ridges

show up under this lighting. These are thought to be the result of com-

pressional forces.

Further out, crossing the junctions of the Mare Humorum and Palus

Epidemiarum and Mare Nubium, are several, also roughly concentric,

graben. Each is of the order of 55 km wide and extends several hundreds of

kilometres in length. These slumped features are thought to be the result

of crustal stretching. Notice how they even carve their way through the

mountainous regions and the oldest of the craters (but not the youngest

examples).

The cluster of craters at the southern periphery of Mare Humorum are

particularly beautiful. Figure 8.22(c) shows the group. It is an enlarged

portion of Figure 8.22(a). The easternmost of the main craters, and the least

degraded, is Vitello. Vitello is 45 km across and 1.7 km deep in its complex


Figure 8.22 (cont.)(f) Gassendi at colongitude48°.7. Details in text.(Courtesy Lunar andPlanetary Laboratory.)(g) Gassendi at colongitude61°.0. Other details in text.(Courtesy Lunar andPlanetary Laboratory.)

(f) (g)

interior. It has a central hill and the interior shadows are far from regular

when the Sun is low, as can be seen in the fine study by Andrew Johnson

presented in Figure 8.22(d).

To the west of Vitello is the remnant of a large lava-flooded crater, with

another partial ring, again completely flooded, abutting to its south-west.

In effect, these form ‘bays’ in the Sea of Moisture. Just to the north-west of

these and, at 64 km diameter, the largest of the formations pictured in

Figure 8.22(c) is Dopplemayer. It has been flooded and eroded and yet its

lofty central mountain soars about 760 m above the rippled floor of the

crater.

It is Gassendi, though, which is the real jewel of the Mare Humorum.

Spanning both ‘shore’ and ‘sea’ on the northern sector of the mare this

110 km diameter ‘ring-plain’ formation appears like a black lake at the

times when the morning and the evening terminator just reaches it (see

Figure 8.22(e)). With the Sun at a higher angle, the interior is seen to be


Figure 8.22 (cont.)(h) Orbiter V photograph ofGassendi. (Courtesy NASAand Professor E. A.Whitaker.)

(h)

highly complex. Figure 8.22(f) shows a photograph of it taken with the 1.5 m

Catalina Observatory telescope on 1966 April 2d 08h 12m UT when the Sun’s

selenographic colongitude was 48°.7. Figure 8.22(g) shows it under a higher

Sun (selenographic colongitude 61°.0). In fact, Figure 8.22(g) is an enlarged

portion of part of Figure 8.22(a). You might notice how the relative promi-

nence of the interior features has altered quite considerably over what is a

relatively small change of lighting angle. This, in addition to the overall

complexity of the formation, led to the selenographers of old varying quite

considerably in the way they represented the crater. Inevitably, this led to

debates about possible physical changes to the crater during the lifetimes

of the observers – an idea now long abandoned, I hasten to add.

The walls vary in height around the crater, being highest on the west.

An average height for them is about 1.8 km above the crater floor. The crater

Gassendi A (33 km diameter, 3.6 km deep) intrudes into Gassendi to the

north. Gassendi A is rather hexagonal in outline and has a complex inter-

ior. The southern section of the wall of Gassendi is highly eroded and even

gives the impression of having been melted down by the lavas of Mare

Humorum. The mare materials have clearly entered the crater here. The

average hue of the floor of Gassendi is lighter than that of the Mare

Humorum, except for the smooth crescent-shaped sector originating at the

wall breach, which is of the same shade.

The crater floor is of the order of 600 m higher than the average level of

the outer surrounds and is criss-crossed by a remarkable network of rilles.

Many of these are visible in quite small telescopes (80–100 mm aperture)

under suitable conditions of lighting. For a really detailed view of Gassendi

take a look at the Orbiter V photograph shown in Figure 8.22(h).

As well as having a network of rilles over it, the floor is also rather rough

and hummocky and there is an impressive central mountain complex. This

is really the remnants of a central ring, as is evident in Figure 8.22(h). The

tallest of the central peaks soars to above 1 km in height.

Gassendi is one of the Moon’s ‘hot spots’ of Transient Lunar

Phenomena, with many reliable reports of bright flashes and red glows

seen in the crater. Significantly it turns out that it is also one of the sites of

enhanced radon emission.

What story does the craggy face of Gassendi have to tell? Has the inter-

ior been pushed upwards by forces from below? What are the order and the

time-scales of the events that have led to the Gassendi we see today?

8.23 HYGINUS, RIMA [CENTRED AT 8°N, 6°E] (WITH HYGINUS, RIMAE

TRIESNECKER, TRIESNECKER)The current thinking about rilles is that they are of two distinct types, each

with a different mechanism of formation. Sinuous rilles are thought to have

8.23 HYGINUS, RIMA 243

been formed by running lava. Possibly the lava cut across the surface of the

mare (they are peculiar to maria), or maybe it cut a tunnel just under the

surface – the roof of the tunnel collapsing at a later date. They are charac-

teristically about 1–2 kilometres wide (but wider examples exist, such as

Vallis Schröteri) and they tend to snake about in the same manner as rivers

do here on Earth.

The other type are the linear rilles. These tend, as their name suggests,

to be somewhat straighter. Any changes of direction are rather more

angular than is the case for the sinuous rilles. They also tend to be wider,

typically 5–60 km, and can cross mare and highland boundaries. They are

evidently lineaments where the ground to either side has been pulled

apart slightly, creating slumped channels.

We call any channel of this sort a graben. Rima Ariadaeus, discussed in

Section 8.6, seems to be of this type, and the arcuate rilles on the junction

between the Mare Humorum and Palus Epidemiarum (see Section 8.22)

even more definitely so.


Figure 8.23 Triesneckerand its associated rilles(upper-right) and RimaHyginus (extending frommiddle left to lower right)photographed using the1.5 m reflector of theCatalina Observatory. Atthe time of the exposure,1966 May 27d 03h 56m UT,the Sun’s selenographiccolongitude was 356°.8.(Courtesy Lunar andPlanetary Laboratory.)

Look at Figure 8.23 and you will find examples of both types of rilles.

This Catalina Observatory photograph is of the region of the Moon extend-

ing from the Sinus Medii (at upper right) to the Mare Vaporum (lower left).

Near the upper right of the frame is the 26 km diameter crater Triesnecker.

It is itself an interesting object, 2.7 km deep and with a central mountain

complex. However, it is the system of rilles extending from its eastern flank

that grab the attention. These are the Rimae Triesnecker. They seem to be

of the sinuous variety.

Crossing much of the frame from the lower right to the middle left

of Figure 8.23 is the very much more prominent Rima Hyginus. At the

extreme left of the photograph you will see the ‘tail end’ of another rille

running parallel to the eastern end of the Rima Hyginus. This is the Rima

Ariadaeus already referred to, and discussed more fully in Section 8.6.

Notice how a small crater (it is 10 km across) is situated at the sharp

bend in the rille. This is the crater Hyginus. It is deeper than the rille and

extends to a depth of about 770 m. Look carefully at the section of the rille

to the east (left in the photograph) of Hyginus and you will see further,

though much smaller, craters threaded along it like pearls on a necklace.

High-resolution images from space probes reveal even more of the crater-

chain appearance of Rima Hyginus. Other linear rilles show a similar

structure.

It is not easy to understand exactly how these craters fit into the scheme

of things. Are they also collapse features? Could at least some of the ‘linear

rilles’ have been created in the same way as the sinuous rilles, except that

the underground channels were much wider. Perhaps there was extensive

lava flowing in thin sheets underneath the freshly solidified surfaces of the

mare? Perhaps the roof falling in at widely spaced intervals creates crater

chains? (Please note, I am here just referring to the small craters associated

with rilles. I am not seeking to revive the spent arguments about the crea-

tion mechanisms of the Moon’s major craters!) If the roof-falls occur closer

together do they then form rilles of the Hyginus type? What about the

crater Hyginus, itself, though? It is much deeper than the rille of which it

seems to be such an important part.

If I seem to have posed a lot of questions to which you think that we

ought to have definite answers by now, then I can only say that many

experts differ in their interpretations of the rilles – and a few openly say

that they are not at all sure of the mechanisms that have created these

intriguing features.

The Ariadaeus, Hyginus and Triesnecker rille systems are visible with

quite small-aperture telescopes near the times of first and last quarter

Moon. I heartily commend you to seek them out and ponder on their sig-

nificance for yourself.

8.23 HYGINUS, RIMA 245

8.24 IMBRIUM, MARE [CENTRED AT 35°N, 345°E] (WITH ARCHIMEDES,ARISTILLUS, AUTOLYCUS, BIANCHINI, HELICON, MONTES JURA,PROMONTORIUM HERACLIDES, PROMONTORIUM LAPLACE, SINUS

IRIDUM, TIMOCHARIS)The eastern edge of the Mare Imbrium (Sea of Rains) begins to come into

sunlight about a day before first quarter Moon. At first quarter the area

takes on a grand spectacle, as the photograph by Tony Pacey in Figure

8.24(a) shows. However, the nature of this important feature is probably

best appreciated at a lunar age of about 10–11 days. Figure 8.24(b) is a photo-

graph I took under just such lighting and conditions. I used my 181⁄4-inch

(0.46 m) reflector to image the Moon directly onto HP5 film (processed

in ‘Celer Stellar’ developer) in the camera mounted at the telescope’s

Newtonian focus (no eyepiece). Hence the effective focal ratio (EFR) is

simply the focal ratio of the telescope (f/5.6).

If my choice of film seems odd to you, the reason is that I had wanted to

use image projection to a high effective focal ratio. Hence the high-speed

film I had loaded into my camera. As it was, the night turned out to be

totally unsuitable, with poor transparency and very bad atmospheric turbu-

lence, so I contented myself with a couple of low-resolution photographs of

the Moon. The 1/500 second exposure was made at 1978 July 15d 21h 23m UT,

when the Sun’s selenographic colongitude was 25°.3.

Figure 8.24(b) shows the outline of the circular Mare Imbrium very well,

only the westernmost extremity of it lying over the dark side of the termi-

nator. This basalt-filled basin is a whopping 1250 km in diameter. Only

the Oceanus Procellarum has a greater area of mare-type basalt and the

Imbrium Basin is the largest that is clearly identifiable as such on the Moon

today. The impactor that created the basin also created ejecta and a pattern

of ridges and linear faults radial to it that can be discerned (if you know

what to look for) covering a large part of the Moon’s visible face. Some of

these have been featured in other sections in this chapter.

Several of the Apollo missions have obtained samples which included

those identified as Imbrium impact ejecta (and Apollo 15 actually landed on

the periphery of the Mare Imbrium). It is from the laboratory analysis of

these samples that a fairly precise date has been determined for the basin-

creating impact. The results indicate that it happened 3.85 billion years

ago, the uncertainty being plus or minus 0.05 billion years. This is one of

the primary benchmarks that has been used to build up our picture of the

sequence of events which sculpted the surface of the Moon that we see

today. Actually, the Imbrium Basin is the youngest of the really large basins

on the Moon’s Earth-facing hemisphere. The Orientalis Basin is the only

large one that is younger, but very little of it shows on the Earth-facing

hemisphere.


The age of the surface covering of the Mare has been determined mainly

by the method of counting the numbers of craters of specific sizes, keyed

with the determined ages of the Apollo 15 rock samples. That and spectro-

photometric studies (reflectance at specific wavelengths) has shown that

episodes of lava flooding occurred from 3.7 to 3.2 billion years ago. The

lavas that form the major part of the visible surface of the Mare Imbrium

are taken to be about 3.3 billion years old.

8.24 IMBRIUM, MARE 247

Figure 8.24 (a) Sunrise overthe Mare Imbrium photo-graphed by Tony Pacey on1987 April 6d 20h 00m UT(approx.). He used his10-inch (254 mm) reflector,with eyepiece projectiononto Ilford FP4 film for this0.25 second exposure.

(a)

Some of these lava flows are visible as areas of slightly differing hue,

even to the observer using simple eyeball-to-eyepiece methods. You might

like to try looking for these yourself.

As always with lunar maria, a low Sun-angle shows up many wrinkle

ridges and a peppering of small craters also covers the mare, though most

are beyond the powers of amateur-sized telescopes and normal backyard

observing conditions. See what examples you can find.

Figure 8.24(c) shows the south-eastern sector of the mare, while Figure

8.24(d) shows its north-eastern sector. Both are photographs taken with the

1.5 m reflector of the Catalina Observatory in Arizona. Figure 8.24(c) was

taken on 1967 January 20d 01h 46m UT, when the Sun’s selenographic colon-

gitude was 18°.5 (morning illumination) and Figure 8.24(d) was taken on

1966 September 6d 10h 44m UT, when the colongitude was 167°.3 (late after-

noon).

The spectacular Montes Apenninus defines the south-eastern boundary

of the mare (see Figure 8.24(c)). These are chiefly blocks of lunar crust

which have been violently uplifted by the Imbrium impact event. This

mountain range is discussed in more detail in Section 8.5, earlier in this


Figure 8.24 (cont.)(b) The circular outline ofthe Mare Imbrium isevident in this photographby the author. Details intext.

(b)

chapter, together with the crater Eratosthenes, which marks the northern-

most point of the Apennine range. To the west of Eratosthenes lies a

further, smaller, range of mountains, the Montes Carpatus, with the major

crater Copernicus just to their south (see Section 8.13).

The major part of the eastern boundary of the old basin is marked by

the Montes Caucasus, another uplift-created mountain range. Between the

Montes Apenninus and the Montes Caucasus there is a breach in the moun-

tains where mare lavas have flowed to connect the Mare Imbrium with the

adjacent Mare Serenitatis. Figure 8.24(a) shows this particularly well.

Along the north of the Mare Imbrium lies another mountain range, the

Montes Alpes (discussed along with the Vallis Alpes, in Section 8.3). You will


Figure 8.24 (cont.)(c) South-eastern MareImbrium, bordered on theleft by the MontesApenninus. The largestcrater (at the bottom of thephotograph) isArchimedes. The crater toits left is Autolycus andthat to its right isTimocharis. Further detailsin text. (Courtesy Lunarand Planetary Laboratory.)

(c)

notice that the innermost boundary of this mountain range is also concen-

tric with the mare but it lies along an arc of smaller radius than the Montes

Carpatus, Apenninus, and Caucasus. Actually the Imbrium Basin was a

‘multi-ring’ basin. The outermost ring is defined by the mountain ranges

previously mentioned while the Montes Alpes is the surviving part of the

middle one of three original rings of uplifted lunar crust. All that survives

of the innermost ring is a few isolated mountains that poke up through the

lava flood-plain. I will leave you to obtain a map of the mare (I recommend

using a plan-view) and identify, and plot, the vestiges of the rings for

yourself.

There is almost no sign of any remaining ring-relics along the western-

most boundary of the Mare Imbrium. Here it simply merges with the vast


Figure 8.24 (cont.)(d) North-eastern MareImbrium, bordered on theleft by the MontesCaucasus, and on thelower left by the MontesAlpes. Further details intext. (Courtesy Lunar andPlanetary Laboratory.)

(d)

expanse of the Oceanus Procellarum. Examine the area at full Moon and

you will see clear indications that the darker Imbrium lavas have over-

flowed into the slightly lighter Procellarum lavas, rather than the other

way round.

In the bay at the southern extremity of the Montes Alpes and the north-

ernmost section of the Montes Caucasus is situated the interesting crater

Cassini. This crater and its environs are discussed in detail in Section 8.11.

The prominence of the largest crater on the mare, the 83 km diameter

Archimedes, is such as to be a ‘focal point’ of the mare even though it is

positioned considerably off-centre. Figure 8.24(e) (which is an enlarged part

of Figure 8.24(d)) shows it very well. Clearly the impact that created the

crater happened after the Imbrium Basin was formed (it could not have sur-

vived the Basin-forming event) but before the mare flooding episode (the

mare lavas remain undisturbed right up to where the crater emerges from

the mare). It also indicates the shallowness of the mare flood-plain. Most of

this form of crater exists as a depression below the surface of the surrounds

(there are plenty of examples all over the Moon to bolster this assertion).

Yet the rim still rises up to nearly 1.9 km above the flood-plain in places.

Notice, also the hummocky tract of ground extending southwards towards

the Montes Apenninus and how the mare lavas have interacted with it – a

further indication of the shallowness of the lunar ‘sea’. Even at the centre


Figure 8.24 (cont.)(e) Archimedes (the largestcrater), Autolycus (upper-left crater), and Aristillus(lower-left crater). Enlargedportion of Figure 8.24(d).(Courtesy Lunar andPlanetary Laboratory).

(e)

of the Imbrium Basin, the depth of mare basalt is probably no greater than

1.5 km.

The fact that Archimedes has been filled in with mare-type lava almost

to the level of the Mare Imbrium surrounds (actually, about 200 m below)

is interesting. I estimate that the lava-filling inside the crater must extend

to around 2 km depth, deeper than the extreme depths of almost all of the

Moon’s ‘seas’!

Though the crater superficially has a bland appearance, there are some

delicate features to discern in Archimedes. The easiest of these is the spire-

like shadows cast by the crater rim across the floor when the Sun-angle is

low. These are instructive as they are a magnified (though distorted) profile

of the rim itself. The next easiest to discern is a faint pattern of east–west

bands covering the floor of the crater. They are most obvious under a high

Sun. What do you think caused the pattern? Hardest to see are some very

tiny craters within Archimedes. They are best under a low Sun but also

need a good telescope and fine seeing conditions. The ones I have seen most


Figure 8.24 (cont.)(f) Sinus Iridum, borderedby the Montes Jura. Detailsin text. (Courtesy Lunarand Planetary Laboratory.)

(f)

often are a pair close to the north-west rim. I find I can discern some others

but only rarely. How many can you see?

The next major crater to the west of Archimedes (to the right of

Archimedes on Figure 8.24(c), both craters being near the bottom of the

photograph), is the 35 km diameter Timocharis. It is 3.1 km deep, with ter-

raced walls rising to a sharply defined rim. It has a faded ejecta pattern

which becomes most prominent near full Moon. At these times the crater

also takes on a rather ‘mist-filled’ appearance, the same mirage that afflicts

Eratosthenes.


Figure 8.24 (cont.)(g) ‘The Golden Handle’effect. South is to the rightin this drawing by RoyBridge.

(g)


Figure 8.24 (cont.)(h) Promontorium Laplace,drawn by Andrew Johnson.

(h)

The first major crater to the east of Archimedes is Autolycus. This is

39 km in diameter and 3.4 km deep. It has a ray system which is fainter than

that of Timocharis, with a gentler interior slope and wider terraces. To the

north of Autolycus is the larger, 55 km diameter, Aristillus. It is 3.6 km deep

and also has significant interior terracing. Its ray pattern is the most prom-

inent of the three craters. The prominent triple mountain peaks rise to

almost 1 km above the crater floor. All three of these craters have raised

outer slopes and ejecta patterns splashed across the mare, so they were

obviously formed after the mare-flooding episode.

At the western end of the Montes Alpes there is a bay, the Sinus Iridum

(Bay of Rainbows), the bordering mountain range being named Montes Jura

(the Jura Mountains). This bay merges with the Mare Imbrium at the

junction between it and the Oceanus Procellarum. Obviously the Jura

Mountains are the surviving remnants of the uplifted crust defining

another impact basin, of about 250 km diameter, which overlapped the

Imbrium Basin. Which, though, came first? The answer is not at all obvious

but planetologists consider the wide tract of light-coloured, hummocky,

terrain along the northern ‘shore’ of the Mare Imbrium and extending to

the Jura Mountains and a little beyond to have been created contempora-

neously with the Imbrium impact. If this is correct then it follows that the

Iridum Basin was formed after the Imbrium Basin (can you see why?).

Figure 8.24(f) shows the Sinus Iridum in full morning sunlight. It is

another Catalina Observatory photograph, this one taken on 1967 January

22d 03h 31m UT, with the Sun’s selenographic colongitude 43°.9. The cape

at the eastern end of the Montes Jura has been named Promontorium

Laplace (Cape Laplace). That at the western end is Promontorium

Heraclides (Cape Heraclides). The large (39 km diameter) crater in the hin-

terland mid-way between the capes is called Bianchini. The crater at the top

left of Figure 8.24(f) is Helicon. It has an unusual structure, 25 km in diam-

eter with a single interior terrace in the 1.9 km high walls above the flooded

crater floor. Helicon actually resides beyond the boundary of the Sinus

Iridum, on the Mare Imbrium. Many wrinkle ridges cross the floor of the

Sinus Iridum. Some of these are roughly concentric to the Iridum Basin,

others to the Imbrium Basin. The junction between the two is the most

wrinkled part of all.

At the times when the terminator bisects the Sinus Iridum, part of the

Montes Jura are in full sunlight, and the rest of the range pokes up into the

sunshine, producing an effect called “The Golden Handle”. I captured this

appearance in the photograph presented as Figure 8.24(b). A more detailed

view is provided by Roy Bridge in his drawing, which is shown in Figure

8.24(g). Figure 8.24(h) shows a more detailed view of the Promontorium

Laplace at local dawn, as drawn by Andrew Johnson.


Lastly, I should mention the ‘Great Black Lake’ crater Plato which is sit-

uated at the north point of the Mare Imbrium. It is important enough to

demand a section all of its own. You will find details of it and some of the

nearby features on the Mare Imbrium, such as Mons Pico and Piton, in

Section 8.33 further on in this chapter.

8.25 JANSSEN [45°S, 42°E] (WITH FABRICIUS, METIUS, RHEITA, VALLIS

RHEITA)The crater-ridden south-eastern highlands of the Moon can be a highly con-

fusing place to find one’s way around. Figure 8.25(a) is a wide-field view of

this portion of the lunar disk, taken with the 1.5 m reflector of the Catalina

Observatory in Arizona. The exposure was made at 1966 June 24d 03h 39m UT,

the Sun’s selenographic colongitude being 339°.8 at the time.

Look to the left of centre on Figure 8.25(a) and you should be able to

discern the outline of one of the most important formations in this

area of the Moon. This is the crater Janssen (not to be confused with

Jansen – a small crater in the Mare Tranquillitatis!). Figure 8.25(b) is an

enlarged portion of the same photograph, in which Janssen nearly fills

the frame.

Janssen’s hexagonal outline is a mighty 190 km in diameter. It is clearly

an extremely old structure, having been extensively modified and covered

in craters large and small. The largest of the intruding craters, at 78 km

diameter, is Fabricius. This is sited in Janssen’s north-east sector. Notice the

partial inner ring, concentric with the terraced walls of Fabricius. Also of

note is the rille (judging by the look of it, a graben) that curves from the

south-south-west rim of Fabricius right across the floor of Janssen to its far

wall. The whole interior of Janssen has the decidedly ‘tortured’ appearance

of a lunar formation of the greatest antiquity. You will find endless hours

of interest in the study of this one feature alone.

Adjoining Fabricius to its north-east is the somewhat larger (88 km

diameter) crater Metius. Though part of it is seen in Figure 8.25(b), it is seen

fully in Figure 8.25(c), another enlarged portion of the same Catalina

Observatory photograph.

Metius has a much more ‘smoothed down’ appearance than Fabricius,

especially in its floor. Undoubtedly this has much do with the shaking

Metius received during the impacts that created the craters around it, espe-

cially Fabricius which clearly post-dates it. Figure 8.25(a) shows that many

of the old impact-craters share the same eroded characteristics in this

region of the Moon. Going further north-east there is another old crater,

Rheita. This is 70 km in diameter and its general form seems to be some-

thing of a cross between that of Fabricius and that of Metius (but more like

that of Metius).


However, the main interest here is not Rheita but rather the enormous

gorge-like valley its western rim intrudes into. This remarkable formation

dominates Figure 8.25(c).

Depending on where you define the beginning and end of the valley to

be, it is about 180 km long and is about 25 km wide along much of its

length. Best seen two or three days after full Moon, it resembles a line of

craters, all overlapping and with the walls between them broken down.

Both camps of crater creationists (impact and volcanism) claimed

this feature as definite proof of their ideas. To the ‘volcanists’ the valley

8.25 JANSSEN 257

Figure 8.25 (a) The south-eastern highlands of theMoon. Note the hexagonalform of the giant craterJanssen, just to the left ofthe centre of the photo-graph, and the gorge-likeVallis Rheita, close to theleft. Details in text.(Courtesy Lunar andPlanetary Laboratory.)

(a)

258

Figure 8.25 (cont.)(b) Close-up of Janssen.This is an enlarged portionof (a). The crater Fabriciusis in the lower-left part ofJanssen. (Courtesy Lunarand Planetary Laboratory.)

(b)

8.25 JANSSEN 259

Figure 8.25 (cont.)(c) Close-up of VallisRheita. The crater Rheitaintrudes into the lowerend of the valley. Upperright of Rheita, and on theother side of the valley,the largest crater is Metius.Adjoining Metius, and tothe upper right of it, is thecrater Fabricius. Part ofJanssen is also shown inthis enlarged portion of(a), which also overlapswith the view shown in (b).(Courtesy Lunar andPlanetary Laboratory.)

(c)

represented a chain of calderas aligned over a massive fault. Meanwhile

the ‘impactists’ thought that the Vallis Rheita, and a few other examples

of the same type of formation, were created by blocks of material ejected

from the mare basins when they were formed.

It now seems pretty certain that the ‘impactists’ have got it right. The

closest mare is Mare Nectaris and there are a number of less prominent

valleys in the area which are radial to it. You might like to examine Figure

8.25(a), or better still use your telescope to observe the region. How many

valleys can you find?

The commentators I have read who make reference to the creation of

Vallis Rheita all say that the ejecta from the Nectaris Basin event is respon-

sible. However, Vallis Rheita seems to lie at a slightly different angle to the

valleys I can identify as being radial to the Mare Nectaris. I, at least, think

that the impact event that created the Mare Imbrium is the culprit for this

particular ‘scar’ on the lunar surface. Certainly the alignment seems to

better fit the centre of the Mare Imbrium, rather than the centre of the

Mare Nectaris.

I think that the Moon-shaking Imbrium impact of 3.85 billion years ago

caused some huge blocks of material to be blasted from the site into ballis-

tic trajectories. If I am right, one meteor-like collection of these splattered

across the Moon, like a blob of paint from a flicked paintbrush, to create

the valley. Hence the valley is really a secondary impact feature!

8.26 LANGRENUS [9°S, 61°E] (WITH ANSGARIUS, HOLDEN, KAPTEYN,KÄSTNER, LAMÉ, LOHSE, LANGRENUS A, LA PÉROUSE,VENDELINUS)

The splendid crater Langrenus is situated on the eastern shore of the

Mare Foecunditatis. It is large and looks imposing when the terminator is

nearby. It also has a bright interior and so readily stands out under a high

Sun. In fact, Langrenus is striking whenever it is sunlit (see Figure 8.26(a)).

It is a prominent member of ‘the Great Eastern Chain’ of craters, the

most southerly member of which is Furnerius. Going northwards from

Furnerius, first comes Petavius (Furnerius and Petavius are detailed in

Section 8.17), then Vendelinus (see Figure 8.26(b), where it is pictured with

Petavius) and then Langrenus (see Figure 8.26(c), where Vendelinus and

Langrenus are pictured together). The more northerly members of the

‘chain’ are the Mare Crisium (see Section 8.14) and Endymion (see Section

8.15).

The details for Figures 8.26(a) and (b) are given in the accompanying cap-

tions. Figure 8.26(c) is a Catalina Observatory photograph, taken with the

1.5 m reflector, on 1966 May 6d 08h 12m UT. At the time of the exposure the

selenographic colongitude was 103°.4.


8.26 LANGRENUS 261

Figure 8.26 (a) Generalarea of Langrenus (south isdiagonally towards theupper right in this view).Photograph taken by theauthor, using his 0.46 mreflector, on 1977 August29d 22h 33m UT, when theSun’s selenographic colon-gitude was 85°.3. Eyepieceprojection was used (EFR�

f/17) for the 1/30 secondexposure on FP4 film,developed in Microphen.(b) Vendelinus (lower for-mation) photographed,with Petavius, by TonyPacey on 1992 January 21d

23h 55m UT, when theSun’s selenographic colon-gitude was 103°.6. Tonyused eyepiece projectionon his 10-inch (254 mm)Newtonian reflector toproduce an EFR of aboutf/50. A 1⁄2 second exposurewas given on FP4 film.

(a)

(b)


Figure 8.26 (cont.)(c) Langrenus (lower crater)and Vendelinus (the large,less well-defined formationin the upper part of theframe). Details in text.(Courtesy Lunar andPlanetary Laboratory.)

(c)

Langrenus’s roughly terraced walls rise to about 2.7 km above the hilly

floor. Rim-to-rim it spans a diameter of 132 km. The walls may look much

higher than 2.7 km, in relation to the crater’s diameter, but this is an illu-

sion caused by a combination of our foreshortened view of the crater and

the very gentle slope of the inner terraces. Owing to the interior slope, the

main floor arena of the crater spans about 87 km, much smaller than its

rim-to-rim diameter. The prominent and somewhat oddly shaped central

mountain rises up to about 1 km above the crater floor.

There is much fine detail in the interior of Langrenus, and in the

complex outer ramparts, to intrigue the observer equipped with even a

quite small telescope. This is especially so as the appearance of the crater

changes quite dramatically as the Sun rises over it. Figure 8.26(d) shows a

view of the crater at a colongitude of only 6°.1 different from that in Figure

8.26(c), and yet the visual differences are obvious.

At high Sun angles I find that the interior of Langrenus takes on a dis-

tinctly yellowish-brown tint, compared to its surrounds. To see the colour

clearly I use a magnification of no more than �144 on my 181⁄4-inch (0.46 m)

8.26 LANGRENUS 263

Figure 8.26 (cont.)(d) Area extending east-wards from Langrenus.Going increasingly leftfrom the top of Langrenusare the major craters:Langrenus A, Kapteyn andLa Pérouse. To the upperleft of La Pérouse is thelarger crater Ansgarius. Tothe lower left of LaPérouse is the old ‘walled-plain’ Kästner. Furtherdetails in text. (CourtesyLunar and PlanetaryLaboratory.)

(d)

reflector. Can you see any colour tint inside Langrenus through your

telescope?

Vendelinus is a very different type of formation to Langrenus, as is

clearly shown in Figure 8.26(c). In fact, you may find it quite difficult to

make out Vendelinus from the general confusion of lumps, bumps and

smaller craters. This feature really only looks distinctive under a low Sun.


Figure 8.26 (cont.)(e) Kästner, drawn by RoyBridge.

(e)

First take a look at the small-scale image of it in Figure 8.26(b) and you

should then be able to trace its outline in the much more detailed view pre-

sented in Figure 8.26(c). This 147 km diameter ‘walled-plain’ is clearly very

old. Indeed, one could argue that it has just begun to lose its identity as a

crater in its own right. Even if you think that is an exaggeration, you must

surely agree that Vendelinus is a crater in an advanced state of ruin.

The largest crater to intrude into it (on its north-east portion) is the

84 km diameter Lamé. This creates the large ‘notch’ in the outline of

Vendelinus which is so very apparent in Figure 8.26(b), Lamé here being

filled with shadow. The other two sizeable craters which encroach onto the

rim of Vendelinus are Holden to the south-east and Lohse to the north-west.

These have diameters of 47 and 42 km, respectively. As is the case with

Langrenus, there is much fine detail within Vendelinus for the enthusiast

to study. The different characters of these lunar neighbours are as instruc-

tive as they are interesting.

Figure 8.26(d) is already referred to as providing another view of

Langrenus. It is another Catalina Observatory photograph, this time taken

on 1966 April 6d 08h 00m UT when the Sun’s selenographic colongitude was

97°.3. It shows the area eastwards of Langrenus. Take a line from the top of

Langrenus, on the photograph, and extend it to the left and it will cut

through three sizeable craters. The first is Langrenus A (diameter 42 km).

Then comes Kapteyn (diameter 49 km). The last is La Pérouse (diameter

78 km). Notice the evolution of the forms of these craters going from the

smallest. To the south-east (upper left in the photograph) is the even larger

(94 km diameter) Ansgarius. To the north-east of La Pérouse is another

ancient ‘walled-plain’ type of crater, the 119 km diameter Kästner. Roy

Bridge has made a fine drawing of Kästner, along with La Pérouse, and this

is presented in Figure 8.26(e).

This has been something of a ‘whistle-stop tour’ of the complex envi-

rons of the grand crater Langrenus. In truth, one could spend a lifetime

making a study of any chosen small part of it!

8.27 MAESTLIN R [4°S, 319°E] (WITH MAESTLIN)Just 120 km south-south-west of Kepler, Maestlin R is normally camou-

flaged by Kepler’s rays. However, at low angles of illumination Kepler’s rays

vanish and features of small vertical relief become prominent. Maestlin R

is an arc of isolated peaks, the only remains of an ancient crater that was

all but obliterated about 3.2–3.8 billion years ago when the lavas that

formed the vast expanse of the Oceanus Procellarum flowed across the

lunar surface.

The remnants of the crater rim span about 60 km. Figure 8.27(a) shows

an excellent drawing of it made by Roy Bridge. The small crater shown on

8.27 MAESTLIN R 265

the drawing is Maestlin. It is rather dish-shaped, being 7.1 km in diameter

and 1.6 km deep.

The main reason I selected this formation as one to feature is not so

much the formation itself but rather that Roy Bridge has made a superb

sequence drawing of sunrise over it. This is shown in Figure 8.27(b).

Sequence drawings like these are highly instructive. Unless you happen to

have a space probe fitted with high-resolution radar-ranging equipment

that you can put into lunar orbit, this technique is the most sensitive avail-

able to you for detecting small variations of surface height. Appearances

change rapidly at the terminator, as Figure 8.27(b) shows very well.

Combined with drawings made on other dates, sunrise and sunset

sequences can be used to generate extremely detailed profiles of lunar


Figure 8.27 (a) Maestlinand Maestlin R, drawn byRoy Bridge. Note thenorth–south orientationof this drawing.

(a)

surface topography. For instance, the drawings in Figures 8.27(a) and (b) can

be used in this way. I will not pretend that your results will be cutting-edge

science and that the professional planetologists will be waiting with bated

breath for your publications. However, as with all your topographic studies

of the Moon, you will get to know parts of the Moon in intimate detail.

8.28 MESSIER [2°S, 48°E] (WITH MESSIER A)Not far from the crater Langrenus, just a little further north and quite close

to the western shore of the Mare Foecunditatis, is situated one of the

Moon’s real oddities: the pair of craters Messier and Messier A. You might

just be able to make them out on Figure 8.26(a), back in Section 8.26

dealing with Langrenus. Figure 8.28(a), presented here, shows them in

much greater detail. This photograph was taken with the 1.5 m reflector of

the Catalina Observatory on 1966 April 6d 08h 00m UT, when the Sun’s selen-

ographic colongitude was 97°.3.

The eastern (left in the photograph) crater of the pair is Messier. It is

rather oval, being elongated in the east–west direction, with dimensions of

about 9 km�11 km.

8.28 MESSIER 267

Figure 8.27 (cont.)(b) Sunrise sequence ofMaestlin R, drawn by RoyBridge. The orientation ofthis drawing can be ascer-tained by comparing it tothe drawing shown in (a).

(b)


Figure 8.28 (a) Messier andMessier A. The westernshore of the MareFoecunditatis is visible onthe right of the photo-graph. Details in text.(Courtesy Lunar andPlanetary Laboratory.)(b) Orbiter V view of Messierand Messier A. (CourtesyNASA and Professor E. A.Whitaker.)

(a)

(b)

Messier A, which used to be called Pickering (I think that it is a pity the

name was changed), is rather oddly shaped. The eastern (Messier-facing)

side of it is flattened, while the western rim is much more pointed in form.

In fact, the crater rim forms the same profile as a hen’s egg! It is about

13 km across at it’s widest part and is of similar east–west length to Messier.

Both craters have highly reflective interiors with dark streaks extending

westwards from the central regions up their west walls. There seems to be

a thin ridge of raised ground extending from the west rim of Messier to the

east rim of Messier A. Figure 8.28(b), an Orbiter V photograph, shows the

craters in more detail.

Even more weird are the two rays which extend, comet-like, westwards

from Messier A. The rays are very prominent under a high Sun. A 60 mm

refractor will easily show them at these times. Remarkably the rays stay

quite prominent even at very low Sun angles, unlike most other lunar ray

systems.

Many of the observers of yesteryear suspected both long- and short-term

changes in Messier and its companion. Certainly they can change in rela-

tive prominence during the lunation but all these changes are purely

optical effects. However, there is one real mystery which surrounds this

pair – how were they formed? On this there is no universal consensus. It

seems certain that both are the result of a very low-angle (probably about

5°) impact of material striking the lunar surface from the east but was it a

case of ‘one lump or two’?

Did the impactor hit the Moon to form Messier, bouncing and finally

dropping again to form Messier A? Or were there two impactors, perhaps

two fragments of a comet, flying side by side? Nobody really knows for sure.

The bright interiors and surviving ray pattern must mean the craters were

formed in the last few hundred millions of years – why not seek them out

yourself and ponder on how they were created.

8.29 MORETUS [71°S, 354°E] (WITH CYSATUS, GRUEMBERGER, SHORT)Moretus stands like a sentinel at the gateway to the Moon’s south polar

region. It is a magnificent crater, 114 km in diameter, with beautifully

sculpted interior terraces. At the centre of the large, arena-like, floor a

central mountain mass rises to a height of about 2.1 km.

Moretus is pictured in Figure 8.29, which is a Catalina Observatory

photograph. It was taken on 1967 January 20d 01h 52m UT, when the Sun’s

selenographic colongitude was 18°.5. As the photograph shows, there are

signs of another crater on the southern slopes of the interior. Oddly, all

that shows are a series of mountain peaks. Could this be a case of a meteor

having struck almost immediately after the great impact which created

8.29 MORETUS 269

Moretus itself? My thinking is that the interior of Moretus would still have

been largely molten and suffering the aftershocks of the primary impact,

so preventing the second crater from fully forming.

The large crater, actually 94 km in diameter, immediately to the north-

west of Moretus is called Gruemberger. It is obviously older than Moretus,

its outline being much more eroded and its floor more extensively cratered.

To the north of Moretus, also encroaching into Gruemberger, is the much

fresher looking Cysatus. Cysatus, of diameter 49 km, has a finely terraced

interior and a very low central mountain. South of Moretus is the 71 km

diameter crater, Short.

The western extremity of the crater Moretus lies on the Moon’s central

meridian – latitude 0° (and 360°) E. That, together with the convergence of

the terminator, enables one to deduce the direction of the lunar south

pole. Of course, whether one can see it or not depends on the libration. I

wonder how long it will be before a lunarnaut makes the trek and is first

to stick a flag in the Moon’s most southerly location?


Figure 8.29 Moretus is thelarge crater in the upper-middle of this CatalinaObservatory photograph.The formation in thelower-right corner is actu-ally part of the craterClavius. Details in text.(Courtesy Lunar andPlanetary Laboratory.)

8.30 NECTARIS, MARE [15°S, 35°E] (WITH BEAUMONT,FRACASTORIUS, PICCOLOMINI, ROSSE, RUPES ALTAI)

Mare Nectaris is a somewhat undistinguished looking basalt flood-plain in

the Moon’s south-eastern quadrant, adjoining the Mare Tranquillitatis.

With the names meaning ‘Sea of Nectar’ and ‘Sea of Tranquillity’ this

region of the Moon certainly sounds delightful!

The region is pictured in Figure 8.30(a). As can be seen from the photo-

graph, Mare Nectaris is somewhat irregular in outline, though its nature

as a lava-filled basin is not too hard to imagine. Its diameter averages about

8.30 NECTARIS, MARE 271

Figure 8.30 (a) The smoothgrey plain in the upper-leftpart of this photograph isthe Mare Nectaris. Therugged mountain range(really an escarpment) tothe right of the photo-graph is known as theRupes Altai. The threemajor craters to the left ofthe mountain range areCatharina (upper), Cyrillus(connected to Catharina)and Theophilus (overlap-ping Cyrillus). Photographtaken by Tony Pacey, usinghis 10-inch (254 mm)Newtonian reflector on1991 March 21d (time onlyapproximately known –circa. 20h 00m UT). He usedeyepiece projection and a1 second exposure onT-Max 100 film, processedin HC110 developer.

(a)


(b)

350 km. The craters Catharina, Cyrillus, and Theophilus are identified on

the photograph but a detailed discussion of these is reserved to Section

8.44, as is the small crater Mädler just to the east of Theophilus.

The Apollo 16 Lunar Excursion Module touched down in the hinter-

lands approximately 300 km west of Theophilus. The rock samples col-

lected were found to be very complex. In many cases the origins of the

samples could not be determined with absolute certainty. This is particu-

larly so in the case of Nectaris Basin ejecta. Bearing that in mind, plane-

tary scientists have assigned an age of 3.92 billion years to the Nectaris

Basin. Even if the sample identifications are correct, then the analytical

techniques used still give an uncertainty of plus or minus 0.05 billion

years for the result.

The interval between the formations of the Nectaris and Imbrium basins

is now defined to be Nectarian Period in the chronology of the Moon. Officially

the age range this represents spans 3.92–3.85 billion years. This was a time

of heavy bombardment – a real lunar ‘Blitzkrieg’. During the Nectarian

Period a dozen other basin-forming impacts occurred, together with many

of the larger, and now degraded, craters and some light plains formed by

basin ejecta and a general heavy reworking of the Moon’s regolith.

Also very evident on Figure 8.30(a) is a vast mountain range (more accu-

rately described as an escarpment) encircling the mare to the south and

west. This is the Rupes Altai, actually the surviving section of a ring that

must have surrounded the Nectaris Basin until soon after its formation.

The Nectaris Basin was a multi-ring structure. The best-preserved example

of this type of formation is the larger and younger Mare Orientalis, situ-

ated on the Moon’s western hemisphere and mostly on the hidden side.

Figure 8.30(b) shows the southern section of the Mare Nectaris in more

detail. Notice also that the lighting is from the opposite direction. The major

part of the Rupes Altai is also shown. Figure 8.30(c) is an enlarged section of

(b), concentrating on the Rupes Altai. The whole escarpment spans about

500 km and follows a curve of radius approximately 480 km centred on the

Mare Nectaris. The reason this formation is really best described as an escarp-

ment, rather than a mountain range, is that the peaks are elevated to very

little above the ground to the west. However, the ground falls away sharply on

the side facing into the Mare Nectaris, the average drop being about 1.8 km.

It seems that the Rupes Altai is much more a slump-fault than a range

of uplifted crustal blocks, as is the case for the Montes Apenninus, border-

ing the Imbrium Basin.

The formation is striking even through a small telescope when seen

at lunar ages of around 51⁄2 days and 19 days, though it rapidly loses its

distinctiveness when the terminator moves away from the area. As you

might be able to discern in Figure 8.30(b), there are distinct traces of the

continuation of the ring beyond the southernmost point and round to


Figure 8.30 (cont.)(b) Wide-angle viewencompassing the south-ern half of the MareNectaris and the RupesAltai. The dominant craterat the top of the photo-graph is Piccolomini. Theflooded, incompletelyenclosed, crater at the topof the mare is Fracastorius.The crater Catharina andpart of Cyrillus can beseen to the lower right.Photograph taken with theCatalina Observatory 1.5 mreflector on 1965November 12d 10h 31m UT,when the Sun’s seleno-graphic colongitude was134°.3. (Courtesy Lunar andPlanetary Laboratory.)


Figure 8.30 (cont.)(c) Enlarged portion of (b)showing the Rupes Altai.Piccolomini is mostlyhidden beyond the top-leftcorner and Catharina is tothe lower right. (CourtesyLunar and PlanetaryLaboratory.)

(c)

the east of the Mare Nectaris but these are much less obvious than the

Rupes Altai proper.

The southern portion of the Rupes Altai terminates in a beautifully

sculpted large crater (shown in Figure 8.30(b)). This is the 89 km diameter

Piccolomini. Figure 8.30(d) is another enlargement from (b) and is centred

on Piccolomini. The walls of the crater rise to nearly 4.5 km above the sig-

nificantly convex floor. The walls have very fine interior terraces which are

noticeably smoothed by erosion and landslips. The northern half of the

outer slopes are also rippled with slumps running parallel to the crater

rim. The complicated central mountain mass also shows evidence of land-

slips and much of the floor of the crater is also quite well smoothed. Most

remarkable of all, though, is the intrusion into the crater of the external

terrain to the north of it. Indeed, the terrae seem almost to have ‘poured’

into the crater over its northern rim and even ‘flowed’ some way onto the

crater floor. Clearly, Piccolomini has been subject to some very significant

seismic shaking since its creation. A truly remarkable object.

The lava flooding that created the mare is thought to have occurred

about 3.7–3.8 billion years ago. One of the casualties of these floods was the

crater Fracastorius. This 124 km diameter crater is pictured, along with the

southernmost section of the Mare Nectaris, in Figure 8.30(e). This is an

enlargement of yet another part of Figure 8.30(b). Notice how the northern

wall of the crater has been largely eliminated by the lavas. It seems that this

section has been more than just buried. Rather, much of the original crater

wall has been melted and washed away.


Figure 8.30 (cont.)(d) Enlarged portion of (b)centred on Piccolomini.(Courtesy Lunar andPlanetary Laboratory.)

(d)

The nearby crater Beaumont is a smaller-scale (53 km diameter) cousin of

Fracastorius. In this case there is a small breach in the eastern section of the

wall. The tiny craters that pepper the southern section of the Mare Nectaris,

and the flooded floor of Fracastorius in particular, make an excellent test for

observer, telescope and seeing conditions. How many can you see and record?

The small crater Rosse, 12 km in diameter and 2.4 km deep, situated on

the Mare Nectaris about 70 km to the north of Fracastorius, should be easily

visible in almost any telescope which can honestly sport the title ‘astro-

nomical’. It has a bright interior and is obviously quite ‘fresh’ by the stan-

dards of the local terrain.

All in all, this is a fascinating and highly complex area of the Moon.

8.31 NEPER [9°N, 84°E] (WITH JANSKY)If you really want a challenge, try identifying and observing the crater

Neper. It lies so close to the Moon’s eastern limb that libration often con-

spires to remove it from view just when the lighting is suitable and the sky


Figure 8.30 (cont.)(e) Enlarged portion of (b)showing the southernsector of the MareNectaris. Fracastorius is inthe upper half of the pho-tograph. The muchsmaller, flooded craterBeaumont is to the right.The prominent smallcrater to the lower left ofFracastorius is Rosse.(Courtesy Lunar andPlanetary Laboratory.)

(e)

8.31 NEPER 277

Figure 8.31 (a) Neper is thelarge crater close to thelimb of the Moon in thisYerkes Observatory photo-graph. (Courtesy YerkesObservatory and ProfessorE. A. Whitaker.)

(a)

is clear and steady! Moreover, conditions will only be favourable just after

full Moon. The only other time it is seen under a low Sun-angle is when the

Moon is a very thin crescent. However, then the Moon is very close to the

Sun in the sky. At those times you will only be able to see the Moon against

a twilight sky. Even then, its altitude will be very low and the atmosphere

is bound to be very unsteady. Figure 8.31(a) shows a view made under such

conditions. You may think the photograph does not show very much, even

though the libration was obviously rather favourable for observing this

feature. In point of fact, it was taken with the largest refracting telescope

in the world – the 40-inch (1.02 m) telescope of the Yerkes Observatory


Figure 8.31 (cont.)(b) Neper, drawn by RoyBridge.

(b)

(unfortunately I do not have any further details) and getting a view of the

crescent Moon as good as this is no mean achievement!

Neper is a great formation, 142 km in diameter, with terraced walls and

a central mountain. Roy Bridge has made a superb drawing of this difficult

feature and this is presented in Figure 8.31(b). This time the view is of local

sunset over the crater. Roy even manages to show part of the large crater

Jansky which lies beyond Neper and the easternmost part of which actu-

ally lies beyond 90°E. Jansky is 72 km in diameter.

8.32 PITATUS [30°S, 346°E] (WITH HESIODUS)Pitatus is a beautiful flooded crater on the southern shore of the Mare

Nubium. It is 105 km in diameter, and has highly eroded walls and a pecu-

liarly offset central peak There are some ridges, hills, and rilles on its floor

but all are very delicate objects requiring large apertures and steady

seeing and, very importantly, just the right lighting to show them up.

Figures 8.32(a) to (d) are a series of views at a range of lighting conditions.

Figure 8.32(a) is a drawing by Andrew Johnson showing the formation at

local sunrise (Sun’s mean selenographic colongitude 14°.3 for the period

of the drawing). Figure 8.32(b) is another Andrew Johnson drawing, this

time made at a mean colongitude of 17°.9. Figure 8.32(c) is a Catalina

Observatory (1.5 m telescope) photograph taken at a colongitude of 22°.6

and Figure 8.32(d) is another photograph taken with the same telescope

when the Sun’s selenographic colongitude was 39°.9. Notice the dramatic

changes in the appearance of the formation.

The crater joined to the western flank of Pitatus, shown in Figures

8.32(c) and (d), is the 42 km diameter Hesiodus. The breach in the wall

between these two lunar arenas would be a fascinating place for a lunar-

naut to explore. I wonder who will be the first lucky person to trek between

Pitatus and Hesiodus and when that journey will be made? In the mean-

time, there is much to interest and challenge the backyard telescopist in

these particular lunar formations.

8.32 PITATUS 279


Figure 8.32 (a) Pitatus at acolongitude of 14°.3,drawn by Andrew Johnson.

(a)

8.32 PITATUS 281

Figure 8.32 (cont.)(b) Pitatus at a colongi-tude of 17°.9, drawn byAndrew Johnson. NoteAndrew’s comments, espe-cially that about the trueshape of the crater.

(b)


Figure 8.32 (cont.)(c) Pitatus and Hesiodus.Catalina Observatory pho-tograph, taken with the1.5 m reflector on 1966May 29d 04h 41m UT, whenthe Sun’s selenographiccolongitude was 22°.6.(Courtesy Lunar andPlanetary Laboratory.)(d) Pitatus. CatalinaObservatory photograph,taken with the 1.5 mreflector on 1966December 23d 04h 54m UT,when the Sun’s seleno-graphic colongitude was39°.9. (Courtesy Lunar andPlanetary Laboratory.)

(c)

(d)

8.33 PLATO [51°N, 351°E] (WITH MONS PICO, MONS PITON,PLATO A)

If any one formation on the Moon’s surface is more popular, and conse-

quently more observed, than any other, surely it must be the crater Plato.

It is bathed in sunshine from first to last quarter Moon and, as Figure

8.33(a) shows, appears as a dark oval set into the bright strip of rough

terrain betwixt the Mare Imbrium (Sea of Rains) and the Mare Frigoris (Sea

of Cold). It certainly grabs the attention and Johannes Hevelius named it

“The Great Black Lake”.

Plato marks the northernmost termination of the Montes Alpes,

described in Section 8.24, earlier in this chapter. These mountains are the

surviving remnants of an inner-ring feature in the Imbrium Basin. Hence

Plato is situated on the Basin shelf. Since Plato could not have survived the

Basin-forming impact about 3.85 billion years ago, it must have been

formed after that. Given it is clearly flooded with dark basaltic lava, that

puts its age at no greater than 3.0 billion years if we are correct in our asser-

tion that all the major lava upwelling on the Moon was over by then.

Actually, there is some evidence that minor volcanic activity continued on

the Moon for another billion years, though the evidence is strong that Plato

was formed – and subsequently flooded – in the interval 3.85–3.00 billion

years ago. Perhaps of significance is that the composition of Plato’s lava is

a little different to that of the nearby ‘seas’, as witness its somewhat darker

colouration.

The foreshortening due to its location makes Plato appear oval. Really

it is quite circular and regular in outline, spanning 100 km from rim to rim.

The walls of this arena reach up to approximately 2 km above the level of

the dark floor but the summit peaks are fairly jagged. This is shown to the

most beautiful effect when the Sun-angle is very low over the formation.

Very striking spire-like shadows then extend across the crater floor (see

Figure 8.33(b)). When the crater is very near the terminator the shadows

show changes that are apparent after just a few minutes observation.

In fact, the shadows can reach right across the floor from the wall

casting them to the wall opposite. This is a consequence of the fact that

Plato’s floor is one of the flattest large areas on the Moon’s surface.

Under close inspection (though only needing a small telescope for this)

the walls of Plato shows considerable signs of slumping along its northern

and western sections. Most obvious of these is the huge triangular block,

known as Plato Zeta, which has broken away from the western wall and

slumped inwards, leaving a canyon behind it.

As can be seen in Figure 8.33(a), a number of small craters are situated

on Plato’s dark floor. Their visibility is heavily lighting- and seeing-depen-

dent. With Plato close to the terminator and in good seeing, I have used a

8.33 PLATO 283


Figure 8.33 (a) The craterPlato (centre right) pho-tographed with the 1.5 mreflector of the CatalinaObservatory in Arizona, on1967 January 20d 01h 45m UT,when the Sun’s seleno-graphic colongitude was18°.4. Part of the MareImbrium can be seen abovePlato. Just above Plato isthe outline of a ‘ghostcrater’. On the right side ofit can be seen part of theMontes Teneriffe, while onthe upper part of the ghostcrater is situated MonsPico. Mons Piton is in theupper-left corner of thisframe. The crater Plato A isjust to the lower right ofPlato. (Courtesy Lunar andPlanetary Laboratory.)

(a)

power of �432 with my 181⁄4-inch (0.46 m) reflector and seen them as per-

fectly formed bowl-shaped craters with distinctive interior shadows,

though these shadows are not as intensely black as elsewhere. The largest,

which is just a little off-centre in Plato, is the easiest to see. It is about 3 km

in diameter. The crater south-west of this and the pair (appearing as one in

poorer seeing conditions) to the north-west of the near-central crater are

significantly more difficult. There is a very much smaller crater close to

Plato Zeta, which I have glimpsed only very rarely. You might be able to

make it out in Figure 8.33(a). It is also well shown in Figure 8.33(c), another

of Terry Platt’s superlative CCD images. Terry’s image is even more

amazing when you consider that the lighting is rather higher than the

ideal for viewing their crateriform aspect!

At higher Sun angles these craters usually appear as white disks. In bad

seeing these white disks become white ‘blobs’ which fluctuate rapidly in

visibility. On the worst nights they are completely invisible. Of course, it is

the atmospheric turbulence which causes them to behave in this way. Even

accepting that, a large folklore has been built up about apparently enig-

matic variations in visibility of Plato’s floor craters. Almost all of the major

observers of the past have recorded instances when they considered the

floor craters should be visible and yet are completely absent. Many report

8.33 PLATO 285

Figure 8.33 (cont.)(b) Plato, drawn by RoyBridge.

(b)

a fog-like veil extending over the crater floor and extinguishing the details

of all it covers. In all the nearly 30 years that I have been observing the

Moon, I cannot say with certainty that I have ever seen the craters much

less distinct than I considered they should be for the given seeing condi-

tions. However, I have seen the opposite effect on just a few very rare occa-

sions. For instance, I have been perplexed to see the floor craters as bright

white blobs (the near-central one by far the brightest) through my 61⁄4-inch

(152 mm) reflector when all is fuzzy and violently rippling in ANT. V. seeing!

Yet most other times they are invisible through telescopes small or large

when the seeing is not quite as bad. Puzzling!

Plato is also a ‘hot spot’ for other types of transient phenomena. Flashes

have been occasionally reported; also an apparent blurring of parts of the

crater rim while other parts of the crater remain sharp and clear-cut. I have

seen this effect myself. Coloured glows are sometimes reported extending

along the crater rim. Again I can concur. However, the normal prismatic

effect of the Earth’s atmosphere can produce exactly these effects. The

northern section of the rim of Plato then appears reddish-orange and the

southern section appears blue. Is this the cause in every instance? I think

so, though I did once see a red glow that seemed very different in colour

and extent from the normal spurious colour (which was also present).

Is Plato occasionally the site of genuine TLP or are these variations just

illusions, perhaps caused by the normal intertwining of seeing conditions

and the complex interaction of sunlight with the formation? I think that

is certainly the case in the vast majority of instances. Some people are very

sure that is the case in all instances. In fact, they dismiss all suggestions of


Figure 8.33 (cont.)(c) Plato, imaged by TerryPlatt using his 121⁄2-inch(318 mm) tri-schiefspieglerreflector and StarlightXpress CCD camera (otherdetails not available). Theauthor has applied slightimage sharpening andbrightness re-scaling.

(c)

genuine TLP out of hand. I think there is a case for further study – the type

of study that involves very careful monitoring of Plato through the tele-

scope. I have more to say about TLP research in the final chapter of this

book.

Another effect, that has long ago been demonstrated to be an illusion,

is the apparent darkening of the floor of Plato as the Sun rises higher over

it. Of course, the floor actually brightens with increasing Sun-angles. What

is happening is that the rough surrounds of the crater brighten more

rapidly than its smooth floor, so increasing the contrast. Various light spots

and mottled patterns also appear towards local lunar noon (which is full

Moon, as we see it from the Earth). A lighter sector in the south-west, cov-

ering about one-eighth of the total floor area, becomes especially apparent

8.33 PLATO 287

Figure 8.33 (cont.)(d) Mons Piton, drawn byRoy Bridge.

(d)

at these times – a frequent cause of “mists extending across the floor from

the crater wall” reports from the uninitiated.

Plato’s surrounds are very complex and the nearest sizeable crater is

Plato A, 22 km across, situated about 20 km to the north-west of Plato. It is

shown in Figure 8.33(a). A number of fissures cut through the hinterlands,

most prominent of these being a rille extending eastwards from Plato (the

western termination of which occurs a little east of the flanks of the crater).


Figure 8.33 (cont.)(e) Orbiter IV photograph ofMons Pico. (Courtesy NASAand Professor E. A.Whitaker.)

(e)

The strip of rough ground south of Plato is narrowed by the northern

part of the outline of a ‘ghost crater’ extending southwards onto the Mare

Imbrium. It is mostly visible as a slightly raised ridge in the mare, and is

well shown as such in Figure 8.33(a) and in Chapter 5, Figure 5.3. The

feature is approximately 115 km in diameter.

On the western flank of the ghost crater are a collection of mountain

peaks, the Montes Teneriffe. These reach a height of approximately 2.4 km.

The isolated peak on its southern rim is Mons Pico, also about 2.4 km high.

It is a very reflective object and seems extraordinarily bright when the

upper parts of it catch the sunlight and the immediate surrounds are in

the darkness beyond the terminator. This mountain is also the source of

various alleged changes and anomalous appearances, most probably all

illusory. A remarkably straight line of craters cross the ghost crater a little

to the north of Mons Pico.

There are various other isolated peaks poking up through the lavas of

the Mare Imbrium. Some of these can be seen in Figure 8.33(a). One of the

most notable is Mons Piton, visible in the top-left corner of the photograph.

8.33 PLATO 289

Figure 8.33 (cont.)(f) Plato (lower right) toMons Piton (upper left)photographed using the1.5 m Catalina Observatoryreflector on 1966September 6d 10h 44m UT,when the Sun’s seleno-graphic colongitude was167°.3. (Courtesy Lunarand Planetary Laboratory.)

(f)

It is 2.25 km high. This mountain is another source of reported changes and

odd appearances. Figure 8.33(d) is a drawing of the area made by Roy Bridge

(see also the drawing by Andrew Johnson, shown in Chapter 3, Figure 3.5).

Figure 8.33(e) shows an Orbiter IV view of Mons Pico. Mons Pico and Piton

are shown in Figures 8.33(a) and (f) where they are lit from opposite direc-

tions. Notice how their appearances differ between the two views. Is it any

wonder that the visual observers of yesteryear considered the mountains

subject to change!

8.34 PLINIUS [15°N, 24°E] (WITH DAWES, MENELAUS,PROMONTORIUM ARCHERUSIA, ROSS, MARE SERENITATIS, MARE

TRANQUILLITATIS) In the manner of an ancient gate-keeper, the crater Plinius stands close

to the narrow intersection of the Mare Tranquillitatis with the Mare

Serenitatis. It is shown, near the end of a lunar day, and still on guard, in

Tony Pacey’s excellent photograph, which is presented in Figure 8.34(a).

Perhaps the smaller crater Dawes, standing a little to the north-east (left

and slightly lower in the photograph) is an apprentice guard?

Plinius is actually situated just inside the Mare Tranquillitatis. The

mountainous cape immediately west of Plinius is known as the

Promontorium Archerusia, the name surviving from Hevelius’s map. In his

chart Hevelius named what we now call the Mare Tranquillitatis and Mare

Serenitatis the Pontus Euxinus, meaning “Black Sea”. Neither sea might

actually be black, but there is certainly a very distinct colour difference

between the two maria. Mare Tranquillitatis is clearly very much darker

than Serenitatis and it is much bluer. In fact, I find that it takes on a very

distinct Prussian blue tint when seen at low power through my telescopes

(to repeat yet again, the real colours on the Moon are various shades of

brown – but the eye averages the view as white, so producing apparent

coloured tints in specific features. The colours themselves might not be

true but at least they do indicate the colour differences).

Serenitatis, to me, has the faint greenish colour in common with the

other lunar maria. I ought to repeat that experience has shown me that my

eyes are more sensitive to colours than most (and to my regret I find that

this heightened sense is dwindling with age) and you may well go to your

telescope and fail to see any colours at all. Proper colorimetric studies do

show that the Mare Tranquillitatis is much bluer than the other lunar

maria. This is because the Tranquillitatis lavas are much richer in titanium

than is the norm.

Figure 8.34(b) shows a wide-angle view encompassing both maria that I

took myself. It was taken on colour film and even that shows the Mare

Tranquillitatis as bluer than the other mare. It is a pity that it has to be


8.34 PLINIUS 291

Figure 8.34 (a) Plinius (thelarge crater just belowcentre) and environs, pho-tographed by Tony Pacey.He used his 12-inch(305 mm) reflector for this1⁄2 second exposure onT-Max 100 film on 1992September 16d 23h 55m UT,when the Sun’s seleno-graphic colongitude was139°.5.

(a)

reproduced in monochrome here. The Tranquillitatis Basin is probably the

oldest of the large basins. Certainly it has a much less well-defined shape

than most. It is also masconless. Could that mean the basin was formed at

a time not long after the creation of the Moon, when all but an outer very

thin crust was still molten? If so, the Tranquillitatis Basin probably dates

back about 4.5 billion years!


Figure 8.34 (cont.)(b) The two main darkareas close to the lunar ter-minator are MareTranquillitatis (upper) andMare Serenitatis (lower).The small ‘sea’ attached tothe south (top) of the MareTranquillitatis is the MareNectaris. Photograph takenby the author on 1992September 14d 22h 46m UT,when the Sun’s seleno-graphic colongitude was114°.5. He hand-held hiscamera, fitted with a58 mm lens, to a 44 mmPlössyl eyepiece (EFR�f/7.4)for a 1/1000 second expo-sure on 3M Colourslide1000 film.

(b)

The diameter of the Tranquillitatis flood-plain is very roughly 800 km,

about 20 per cent larger than that of the Mare Serenitatis. In common with

the other lunar maria, the lava flooding commenced about 3.9 billion

years ago (less than a hundred million years after the formation of the

Serenitatis Basin), and successive lava flows are evident on both maria. The

last really significant lava eruptions probably occurred about 3.6 billion

8.34 PLINIUS 293

Figure 8.34 (cont.)(c) Plinius and environs,drawn by Andrew Johnson.

(c)


Figure 8.34 (cont.)(d) Plinius (the large crateron the left), Ross (largestcrater above Plinius) andMenelaus (large crater onthe extreme right) pho-tographed using theCatalina Observatory 1.5 mreflector on 1966 April27d 02h 54m UT, when theSun’s selenographic colon-gitude was 351°.0 (morningillumination). The cape tothe right of Plinius is thePromontorium Archerusia.Notice the rilles extendingfrom it and passing belowPlinius. (Courtesy Lunarand Planetary Laboratory.)(e) Plinius and environs,photographed using theCatalina Observatory 1.5 mreflector on 1966September 4d 10h 38m UT,when the Sun’s seleno-graphic colongitude was142°.9 (afternoon illumi-nation). Other details asfor (d). (Courtesy Lunarand Planetary Laboratory.)

(d)

(e)

year ago. Interestingly, the same titanium-rich lavas that dominate the cov-

ering of the Mare Tranquillitatis also encroach onto the southern half of

the perimeter of the Mare Serenitatis.

Figure 8.34(a) shows many of the wrinkle ridges on the mare superbly

well. Figure 8.34(c) is a drawing of the region executed by Andrew Johnson.

It is usual for compressional features on the lunar maria, particularly the

wrinkle ridges, to be complemented with tensional faults around the

peripheries. These mainly manifest as graben-type rilles. You might expect

the junction between two maria to be especially rich in rilles – and you

would be right! Rilles of the graben variety can, indeed, be found at the

junction of the two maria and these are very well shown in Figures 8.34 (d)

and (e), which are Catalina Observatory photographs.

The various illustrations accompanying this section show a day in the

life of the crater Plinius. Figure 8.34(c) pictures the crater at sunrise, while

Figure 8.34(d) reveals it later on in the local morning, Figure 8.34(e) shows

it in the local afternoon, and Figure 8.34(a) shows it at sunset.

The crater is 43 km in diameter and has quite a sharp rim, 2.3 km above

the hummocky floor. The interior walls are terraced and rather complex,

the outer slopes also being complex and with some radial ridging. The

central mountains are very peculiar and can give the impression of being

a crater under some illuminations, such as that shown in Figure 8.34(d).

Under a very high Sun the central peak becomes rather bright and five

bright, rather fuzzy, streaks extend from the central peak up the interior

terraces. This appearance reminds me of a spoked wheel.

To the north-east of Plinius, a little to the left and slightly below it on

Figure 8.34(a), is the crater Dawes. This, another sharp-rimmed crater,

has a diameter of 18 km. Dawes is also shown in Andrew Johnson’s

drawing (Figure 8.33(c)). The features on its floor are all of low height

and so are rather difficult for the backyard telescope-user to appreciate.

Approximately south of Plinius, and above it in Figures 8.34(d) and (e), is

the 26 km diameter crater Ross. The photographs show the somewhat pecu-

liar profile of this crater. Again referring to Figures 8.34(d) and (e), the large

crater to the extreme right on the photographs is the 27 km diameter

Menelaus.

Menelaus has spectacularly terraced walls which rise 3 km up to a

sharply defined rim. The crater brightens considerably under increasing

Sun-angles. Near full Moon it takes on the appearance of a brilliant white

ring. It also has an asymmetric ray pattern, the chief component of which

is a bright streak which bisects the Mare Serenitatis. Obviously the crater

is no more than a few hundred million years old. The asymmetry of the ray

pattern and the somewhat off-centre interior mountain complex suggest

the impactor arrived at an angle to the surface from the south-east.

8.34 PLINIUS 295

Another area of the Mare Tranquillitatis is discussed in Section 8.45.

The next section details another part of the Mare Serenitatis.

8.35 POSIDONIUS [32°N, 30°E] (WITH CHACORNAC, DANIELL, LACUS

SOMNIORUM, POSIDONIUS A)The 100 km diameter crater Posidonius is situated on the eastern edge of

the Mare Serenitatis (see the last section for more details of this mare) and

at the southernmost junction with it and the inset Lacus Somniorum (Lake

of Dreams). Figure 8.35(a) can be used to identify the crater. It appears in

the extreme top-left corner of this photograph by Tony Pacey. It is also

shown in the wide-angle view presented as Figure 8.34(b) in the last section.

There it appears as the large white disk at the left-hand side of the Mare

Serenitatis, and you can also see how it is positioned at the southernmost

junction of the Sea of Serenity and the Lake of Dreams.


Figure 8.35 (a) Posidonius(crater in top-left corner)to the Moon’s north pole,photographed by TonyPacey. Details given in themain text.

(a)

Nigel Longshaw has made a drawing of Posidonius and this is shown in

Figure 8.35(b). This drawing is already impressive to the casual glance. Look

closely at the hand-written notes accompanying it and you will see that Nigel

used a 31⁄2-inch (90 mm) catadioptric telescope to make the observation! This

puts the use of large-aperture telescopes into a proper perspective. It is the

skill and application of the person behind the eyepiece that really counts.

8.35 POSIDONIUS 297

Figure 8.35 (cont.)(b) Posidonius (maincrater) with Chacornac(adjoining Posidonius tothe upper left) and Daniell(bottom crater), drawn byNigel Longshaw.

(b)

Figure 8.35(a), already referred to, shows the crater illuminated by the

morning Sun. To obtain this photograph Tony Pacey used his 10-inch

(254 mm) Newtonian reflector, with eyepiece projection (enlargement

factor not given) onto T-Max 100 film, processed in HC110 developer. The1⁄2 second exposure was made at approximately 20h UT on 1991 March 21d.

The value of the Sun’s selenographic colongitude was approximately 330°

at the time.

Figure 8.35(c) is a photograph of Posidonius taken with the Catalina

Observatory 1.5 m reflector on 1966 September 4d 10h 03m UT. This time the

crater is shown under late afternoon illumination, the colongitude now

being 142°.6. Figure 8.35(b) shows the formation at sunset (details pre-

sented with the drawing).

If you get a feeling of déjà vu when looking at the illustrations accom-

panying this section, then look back to Section 8.22 and you will see why.

The crater Gassendi seems, superficially at least, almost to be the twin of

Posidonius. Gassendi is just 10 km larger in diameter and each formation

has a smaller adjoining crater. In the case of Gassendi, it is Gassendi A. In

the case of Posidonius, it is Chacornac. The main similarity, though, is in

the interior structures of the craters. Both have hummocky and rille-ridden

floors which give the impression of being pushed upwards by forces from

below.

Since the craters are of similar size, one can assert that the incoming

projectile was endowed with a similar amount of kinetic energy (which


Figure 8.35 (cont.)(c) Posidonius withChacornac and Daniell,photographed using theCatalina Observatory 1.5 mreflector. Details in text.(Courtesy Lunar andPlanetary Laboratory.)

(c)

depends on both the speed and the mass of it), but can the locations of the

two craters also be a factor in determining their final forms? Both craters

lie on basin shelves: the Humorum Basin shelf in the case of Gassendi and

the Serenitatis Basin shelf in the case of Posidonius. My speculation is that

the particular subsurface structure that exists at a basin shelf lends itself

to a Posidonius and Gassendi type of crater, given an impactor of similar

energy.

Concentrating on the fine details of Posidonius, it has a somewhat west-

of-centre crater on its floor. This is the 11 km diameter Posidonius A. On the

east side of this crater is a little ring of mountain peaks. Nigel Longshaw’s

drawing (Figure 8.35(b)) shows them particularly well. Perhaps these are

the surviving remnants of an old, now obliterated, crater? A further moun-

tainous ridge encompasses much of the eastern half of Posidonius. Is this

another old and wrecked crater? As Figure 8.35(c) shows very well, much of

the floor of Posidonius within this arc is raised upwards. Also there is sig-

nificant faulting at the interface between this raised ground and the rest

of the interior of Posidonius. Clearly the history of this crater is not at all

straightforward.

The surrounding walls of Posidonius vary considerably in height, being

at their highest (of the order of 2 km) to the east. The largest crater adjoin-

ing Posidonius is Chacornac. It is 51 km in diameter. It has a very ‘tortured’

interior, though it does seem to have been formed after Posidonius. It is

shallower than Posidonius, the lowest point near the centre being about

1.5 km below the level of the crater rim. As the illustrations all show,

several craters lay on or just north of the northern half of the perimeter of

Posidonius. The most interesting of these is Daniell, shown as the lowest

crater rendered in Nigel Longshaw’s drawing of the area (Figure 8.35(b)). Of

course, all the craters in the area appear foreshortened from the Earth

because of their position on the Moon’s disk. Look carefully at the illustra-

tions and you will see that Daniell is much more oval than the others.

Actually it spans about 30 km in the (roughly) north–south direction but

is only about 23 km wide measured (roughly) east–west! Daniell is about

2.1 km in depth. I will leave you to ponder on the events and processes

which have led to the formation we see today.

8.36 PYTHAGORAS [63°N, 258°E] (WITH BABBAGE)To find out if you can see Pythagoras, first locate the Sinus Iridum. Then

look radially from it towards the limb of the Moon. If the area is in sunlight

you will locate the crater Pythagoras very close to the lunar limb. The crater

is best seen a day or so before full Moon. Before then it will not be sunlit.

After that the higher Sun will cause the details to wash out, especially so

since the sunlight will be coming from approximately the same direction

8.36 PYTHAGORAS 299

as we are looking towards it and thus providing no shadow relief for us to

see.

This 128 km diameter crater would be a magnificent spectacle if it were

further round to our side of the Moon. As it is, it is impressive enough

during that brief window of opportunity each lunation. Andrew Johnson

has made a drawing of this formation under these (sunrise) conditions (see

Figure 8.36(a)). If you are wondering about the sunset view, unfortunately


Figure 8.36 (a) Pythagoras,drawn by Andrew Johnson.

(a)

301

Figure 8.36 (cont.)(b) Pythagoras, pho-tographed using the 1.5 mreflector of the CatalinaObservatory. Details intext. (Courtesy Lunar andPlanetary Laboratory.)

(b)

the Moon is then a waning crescent and will be so close to the Sun in the

dawn sky that the seeing is bound to be bad.

Another view of this crater is provided in Figure 8.36(b). This is a photo-

graph taken with the 1.5 m reflector of the Catalina Observatory in Arizona

on 1966 October 28d 06h 34m UT. The Sun’s selenographic colongitude was

79°.3, the Sun being just a few degrees higher than for Andrew Johnson’s

drawing.

Although foreshortened, it is quite easy to make out the crater’s some-

what hexagonal outline. The spectacular terraced walls soar to 5 km above

the arena-like floor of the formation. Examine the crater closely and you

will find plenty of evidence of substantial landslips. The central mountain

cluster is multi-peaked and reaches up to a height of about 1.5 km.

Upper right of Pythagoras in Figure 8.36(b), and extending into the top-

right corner of the photograph, is the peculiar formation named Babbage.

It seems to be the fusion of two main craters. As well as two large (32 km

and 14 km diameter) craters within it, Babbage also contains much interest-

ing detail. I will leave a detailed study of it to you. This is a fascinating area

of the Moon, though one that is certainly not the easiest for the telescopist.

8.37 RAMSDEN [33°S, 328°E] (WITH RIMAE RAMSDEN)The crater Ramsden, 24 km in diameter and about 2 km deep, is fairly unre-

markable. It is situated on the Palus Epidemiarum, which is itself con-

nected to both the Mare Nubium and the Mare Humorum (see Section


Figure 8.37 (a) Ramsdenand Rimae Ramsden.Catalina Observatory pho-tograph. Details in text.(Courtesy Lunar andPlanetary Laboratory.)

(a)

8.37 RAMSDEN 303

Figure 8.37 (cont.)(b) Ramsden and RimaeRamsden, drawn by RoyBridge.

(b)

8.22). The crater appears in the centre of Figure 8.37(a), which is a Catalina

Observatory photograph. It was taken with the 1.5 m reflector on 1966

December 23d 04h 54m UT, when the Sun’s selenographic colongitude was

39°.9.

The major feature of interest is the system of rilles, the Rimae Ramsden,

associated with the crater. This particular system spans about 130 km but


Figure 8.37 (cont.)(c) Ramsden and RimaeRamsden, drawn byAndrew Johnson.

(c)

the area as a whole is rille-ridden. Figure 8.37(b) shows a sunrise drawing

of the formation by Roy Bridge, while Figure 8.37(c) and (d) are two further

studies made by Andrew Johnson under higher angles of illumination.

Figure 8.37(e) is a photograph obtained by the Orbiter IV probe. Can you

work out the sequence of events that has led to the present vista? I will

leave you to study the area and offer the illustrations here as a starting

point.

8.37 RAMSDEN 305

Figure 8.37 (cont.)(d) Ramsden and RimaeRamsden, anotherdrawing by AndrewJohnson.

(d)

8.38 REGIOMONTANUS [28°S, 359°E] (WITH PURBACH, THEBIT,WALTER)

Regiomontanus inhabits a very complex area of lunar highlands. Being

close to the meridian, the area is perhaps best studied around the times of

last and first quarter Moon.

The region is pictured in Figure 8.38(a), which is a photograph taken

using the Catalina Observatory 1.5 m reflector. It was taken on 1966 May

29d 04h 41m UT, when the Sun’s selenographic colongitude was 22°.6.

Regiomontanus is the large and rather oval formation pictured a little

above the centre of the photograph. It measures 126 km east–west and

110 km north–south. Notice the eroded walls and the floor peppered with

small craters. Does this give you any idea of the age of the crater? The irreg-

ular walls rise in places to about 1.7 km above the floor. The attention-

grabbing feature of Regiomontanus has to be the off-centre ‘central’

mountain with its summit crater. Known as Regiomontanus A, this little

crater is 5.6 km wide and 1.2 km deep. What do you think about its origin?

Below Regiomontanus in Figure 8.38(a), and overlapping it, is the

118 km diameter ‘walled-plain’ Purbach. Its very rough walls extend

upwards to nearly 3 km above the inner arena. Many interesting details

reside inside this formation. What do think about its age?

Above Regiomontanus on Figure 8.38(a) (and not quite completely shown

in this view) is the even larger ‘walled-plain’ Walter. It is also somewhat


Figure 8.37 (cont.)(e) Orbiter IV view ofRamsden. (Courtesy NASAand Professor E. A.Whitaker.)

(e)

8.38 REGIOMONTANUS 307

Figure 8.38(a)Regiomontanus and envi-rons. Catalina Observatoryphotograph. The largecrater at the top is Walter.The large crater below thatis Regiomontanus. Notethe off-centre mountainwithin it, and the moun-tain’s summit crater. Justbelow Regiomontanus,and encroaching into it, isthe large crater Purbach.Near the bottom right ofthe frame are the overlap-ping craters Thebit (thelargest), Thebit A andThebit L (the smallest).Further details in text.(Courtesy Lunar andPlanetary Laboratory.)

(a)


Figure 8.38 (cont.)(b) Regiomontanus andenvirons shortly aftersunrise. Details in text.(Catalina Observatory pho-tograph – courtesy Lunarand Planetary Laboratory.)

(b)

‘squashed’ in the north–south direction; 132 km, as opposed to its east–west

span of 140 km. Its eroded walls rise up to just over 4 km above the rough

and hummocky floor. The walls are very broad and are divided by valleys

along the southern section. Of particular note is the cluster of craters on its

north-east (lower left in the photograph) quadrant. Any ideas on the evolu-

tion of this and the other craters in the area?

8.38 REGIOMONTANUS 309

Figure 8.38 (cont.)(c) Thebit, drawn by NigelLongshaw.

(c)

Figure 8.38(b) is another Catalina Observatory, 1.5 m telescope, photo-

graph. It shows Walter in its completeness. It also shows the area very

shortly after local sunrise, the selenographic colongitude here being 7°.1.

The photograph was taken on 1967 January 19d 02h 45m UT.

In the lower-right corner of Figure 8.38(a) (and (b)) is pictured a rather

beautiful little arrangement of overlapping craters. The largest of these, at

55 km diameter, is Thebit. It is 3.3 km deep and has a rather rough floor. This


Figure 8.38 (cont.)(d) A further study ofThebit, by Nigel Longshaw.

(d)

crater is intruded upon by the 20 km diameter Thebit A. It has a smoother,

almost bowl-like, profile and a small flat floor, at a level 2.7 km below that of

the crater rim. Thebit A is, itself, invaded by a yet smaller crater. This one is

now officially known as Thebit L (you may find other designations elsewhere)

and is 12 km across. It is very shallow and has a tiny central crater within it.

Proponents of the endogenic theories of crater production made much

of this formation in order to support their views. As well as the sequence

of craters of diminishing size supporting their idea of a diminishing scale

of volcanism occurring along a fault to produce the formation, they cited

the undeniable evidence of the perfection of the crater outlines up to the

point of the junction between them. They argued that any explosive event

would have produced a shaking down of the walls of the earlier craters.

However, when we look at lunar craters at much higher resolutions than is

usually obtainable by conventional observations through our atmosphere

we do see a degree of disturbance; enough not to need an endogenic crea-

tion mechanism for the intruding crater. The fact that intruding craters

are almost always smaller than the craters they break into is explained by

the fact that the smaller number of large impactors was more rapidly used

up, leaving the greater number of smaller rocky (and icy?) fragments to

subsequently pepper the Moon. So, the mystery disappears. In fact, there

was never really a mystery at all.

Nonetheless, Thebit has always attracted the attention of observers.

Figure 8.38(c) and (d) are two excellent studies of the formation by Nigel

Longshaw. The whole area is rich in detail and full of interest. I commend

its study to you.

The southern part of the crater rim shown at the bottom of Figure

8.38(a) belongs to Arzachel. I included it so that you might see how this

region connects with that detailed in Section 8.4. Immediately west of

Thebit is the formation known as “The Straight Wall”, more properly the

Rupes Recta. This is discussed in Section 8.43.

8.39 RUSSELL [27°N, 284°E] (WITH BRIGGS, BRIGGS A, BRIGGS B,EDDINGTON, KRAFFT, SELEUCUS, STRUVE)

The crater Russell is situated near the western edge of the Oceanus

Procellarum and is very close to the north-eastern limb of the Moon. Roy

Bridge has made an excellent drawing of sunrise over this formation and

this is presented in Figure 8.39(a). This formation is the remains of an

ancient ‘walled-plain’ type crater, about 99 km in diameter. A wider view

of the area is shown in Figure 8.39(b), in which it can be seen that Russell

is connected, via its missing south wall, to another great ring structure.

This one we now call Struve. In older maps it is called Otto Struve and

Russell is sometimes denoted as Otto Struve A. On other old maps, Russell

8.39 RUSSELL 311

is taken to be part of Otto Struve. As well as A now being called Russell,

the adjoining crater now commemorates all three astronomers Struve

(Friedrich G. Wilhelm von Struve, his son Otto Wilhelm von Struve, and

grandson Otto Struve). It is perhaps appropriate that the crater with three

peoples’ names is so large. It spans 183 km.

Figure 8.39(b) is a photograph taken with the Catalina Observatory 1.5 m

reflector on 1966 October 28d 06h 28m UT, when the Sun’s selenographic


Figure 8.39 (a) Russell,drawn by Roy Bridge.(a)

8.39 RUSSELL 313

Figure 8.39 (cont.)(b) Russell (bottom), con-nected to Struve (large for-mation on the terminator)and Eddington (adjoiningit and sharing its wall withStruve) on the left ofStruve. To the left ofEddington is the craterSeleucus. Above Eddingtonis the crater Krafft. Of thetwo craters near thebottom left, the upper oneis Briggs and the lower(smaller) one is Briggs B.Briggs A is actually on theeastern (left in this photo-graph) rim of Russell.Other details in text.(Catalina Observatory pho-tograph – courtesy Lunarand Planetary Laboratory.)

(b)

colongitude was 79°.3. Notice how the floors of the craters obviously share

the curvature of the Moon’s surface (revealed by the shading). This is hardly

surprising, since they are all flooded with mare lavas.

Figure 8.39(c) is another of Roy Bridge’s splendid drawings. This one

shows the wider area, encompassing Russell (at the bottom), and Struve.

Notice that Roy has included the letter designations of many of the smaller

craters. He has also picked out some radial dark bands running up the


Figure 8.39 (cont.)(c) Russell and Struve,drawn by Roy Bridge.

(c)

interior of the crater Briggs A, situated on the eastern rim of Russell. You

might look for these yourself. Briggs A has a diameter of about 23 km.

Locate Russell, then Briggs A near the bottom of Figure 8.39(b) and

you will see two craters to the left (east) of Briggs A. The upper crater is

Briggs. It is 39 km in diameter and has a most interesting interior. I will

leave its examination to you. The lower one is Briggs B. It is 25 km in

diameter.

8.39 RUSSELL 315

Figure 8.39 (cont.)(d) Russell, Struve (oldname “Otto Struve”) andEddington, drawn byAndrew Johnson.

(d)

Attached to the eastern flank of Struve, and sharing part of its rim, here

significantly enhanced, is another flooded and ruined old ring. On modern

maps this one is called Eddington. Confusingly, on some old maps this

crater is known as Otto Struve A. It is 134 km in diameter. Figure 8.39(d)

shows a splendidly detailed, and yet wide-angle, view of Russell, Struve and

Eddington by Andrew Johnson.

A short distance east of Eddington is the 43 km diameter prominent

crater Seleucus. It is well shown in Figure 8.39(b). Notice the unusual

profile of this crater. It is very deep for its size, the depth being approxi-

mately 3 km.

The prominent crater near the top of Figure 8.39(b) is the 51 km diam-

eter Krafft. Notice the pretty cluster of small craters around it, like bees

around a honey pot.

The notes I have given here are very brief. In common with the later sec-

tions of this chapter, my intention is just to highlight some interesting

areas of the Moon for you to investigate for yourself. I am sure that you will

agree that in this region there is plenty to investigate.

8.40 SCHICKARD [44°S, 305°E] (WITH LEHMANN)Schickard is a vast, partially flooded crater of the ‘walled-plain’ variety. It is

227 km in diameter and is situated near the Moon’s south-eastern limb.

A portrait of this great edifice is presented in Figure 8.40(a). It was taken with


Figure 8.40 (a) Schickard.See text for details.(Catalina Observatory pho-tograph – courtesy Lunarand Planetary Laboratory.)

(a)

the Catalina Observatory 1.5 m reflector on 1966 September 10d 12h 02m UT,

when the Sun’s selenographic colongitude was 216°.8.

BAA Lunar Section members have long been interested in Schickard

and the variety of objects that litter its floor. Probably the selenographer

who has, more than most, made this formation his own is Keith Abineri.

He began his telescopic studies in April 1946 and continues to work at this

feature even to the time of writing these words. Though he no longer uses

a telescope, he applies himself to the examination of Orbiter and Clementine

space-probe imagery. He has published many papers in the BAA Journal and

BAA Lunar Section publications, such as The New Moon. You might like to

search these out for yourself. As well as being interesting in their own

8.40 SCHICKARD 317

Figure 8.40 (cont.)(b) Sunrise over Schickard,drawn by Andrew Johnson.Note the drawing is orien-tated with west veryapproximately uppermost.

(b)


Figure 8.40 (cont.)(c) The southern half ofSchickard, drawn byAndrew Johnson.

(c)

right, you might find some of these instructive with regard to the metho-

dology he adopts.

Figure 8.40(b), (c) and (d) are recent telescopic studies of sections of this

formation undertaken by Andrew Johnson.

A roughly triangular swath of lighter-hue material crosses the floor of

Schickard from the south-west (where it is widest) to the north-east, the

rest of the crater floor being very dark. This appearance is best seen under

a high Sun, though indications of it are visible in Figure 8.40(a).

8.40 SCHICKARD 319

Figure 8.40 (cont.)(d) The northern half ofSchickard, drawn byAndrew Johnson.

(d)

The rim of Schickard is interrupted by various craters and the largest

abutting crater, at 53 km diameter, is the highly eroded Lehmann. It is

shown in the bottom-right corner of Figure 8.40(a).

8.41 SCHILLER [52°S, 320°E]Not far from the giant crater Schickard (see previous section), is a real lunar

oddity. At first glance Schiller appears like a considerably elongated crater.

It is 179 km long and spans 71 km at its widest point. Figure 8.41(a) to (d)

illustrate the crater under a series of lightings from early morning (a) to

sunset (d). They are photographs taken with the Catalina Observatory

1.5 m reflector and the details of date, time and selenographic colongitudes

are given in the accompanying captions. Figure 8.41(e) presents a much

more detailed view, this having been obtained by the Clementine space

probe.

The usual explanation given in print for this formation is that it is the

fusion of two craters. However, I disagree. I think that Schiller was formed

from at least three, possibly four, fused craters or, perhaps, by at least

three, possibly more, large projectiles arriving virtually simultaneously.

My reasoning stems from the outline of the formation. To me, the south-

ern rim has a smaller radius than that of the adjoining main section. The

narrower northernmost section also constricts sharply where it ends


Figure 8.41 (a) Schiller,photographed using the1.5 m reflector of theCatalina Observatory inArizona, on 1966 April2d 08h 03m UT, when theSun’s selenographic colon-gitude was 48°.7. (CourtesyLunar and PlanetaryLaboratory.)

(a)

8.41 SCHILLER 321

Figure 8.41 (cont.)(b) Schiller, photographedusing the 1.5 m reflector ofthe Catalina Observatoryin Arizona, on 1967February 22d 03h 43m UT,when the Sun’s seleno-graphic colongitude was61°.0. (Courtesy Lunar andPlanetary Laboratory.)(c) Schiller, photographedusing the 1.5 m reflector ofthe Catalina Observatoryin Arizona, on 1966January 6d 05h 45m UT,when the Sun’s seleno-graphic colongitude was80°.9. (Courtesy Lunar andPlanetary Laboratory.)

(b)

(c)

in an arc of smaller radius. Moreover, the northern section sports two

‘central peaks’ both of which are highly elongated into ridges running

along the long axis of the southern part of Schiller. The northern half of

Schiller doesn’t quite follow the same axis. It slightly ‘kinks’ a little to

the east.

Putting the, albeit superficial, evidence together, I most favour the idea

that a tight cluster of projectiles, whether they be cometary or asteroidal

fragments, impacted the Moon at a low angle. The direction would obvi-

ously be along the long axis of the formation – but from which direction?

The fact that just the southern end of Schiller has a ‘central peak’ type of

formation might be significant. Was any part of the current formation

already in existence on the Moon before the impacts that created the rest

of it, or was it all formed in one go?

Of course, I must make it very clear that the foregoing is nothing

official. It is merely my speculations on the subject. One thing is certain,

though: there is much more to Schiller than the simple ‘fusion of two

craters’ idea usually peddled. What do you think about it?


Figure 8.41 (cont.)(d) Schiller, photographedusing the 1.5 m reflector ofthe Catalina Observatoryin Arizona, on 1966September 10d 12h 02m UT,when the Sun’s seleno-graphic colongitude was216°.8. (Courtesy Lunar andPlanetary Laboratory.)

(d)

8.41 SCHILLER 323

Figure 8.41 (cont.)(e) Clementine image ofSchiller. (Courtesy NASA.)

(e)

8.42 SIRSALIS, RIMAE [14°S, 320°W] (WITH SIRSALIS, SIRSALIS A)Situated near the Moon’s western limb, the Rimae Sirsalis is just about the

longest of the lunar rilles. Its length is 330 km. It is even more noteworthy

in that it is one of the straightest over such a long length. Most of it is just

one rille, the Rima Sirsalis, but it does have a few branches and extensions.

Hence the more exact name of Rimae Sirsalis.

Figure 8.42 shows the main part of it in a photograph taken using the

1.5 m reflector of the Catalina Observatory, in Arizona. It was taken on 1966

February 4d 07h 02m UT, when the Sun’s selenographic colongitude was

74°.2. The rille can be seen running down the centre of the photograph. It

is a graben; a slump feature. What caused it? The outer fringes of the

Orientalis Basin are not too far away. However, the rille runs neither radial

to it, nor tangential. So, was the Orientalis impact the cause?

Many amateurs have observed this feature as a sport, trying to trace the

limits of its extension north and south. Four serious studies of the rille are

presented here in Figure 8.42(b)–(e). From the first two, they cover sections

going progressively northwards along it.

The significant pair of overlapping craters shown close to the centre of

Figure 8.42(a) are Sirsalis and Sirsalis A. The complete one is Sirsalis. It is

44 km in diameter and is about 3 km deep. The central mountain is small,

really just a hill, but is nonetheless prominent. Sirsalis A is actually slightly

larger, at 49 km diameter, than Sirsalis though it is significantly over-

lapped by Sirsalis.


Figure 8.42 (a) Sirsalis andSirsalis A (the overlappingcraters below the centre)and Rimae Sirsalis(running down themiddle). Details in text.(Catalina Observatory pho-tograph – courtesy Lunarand Planetary Laboratory.)

(a)

8.42 SIRSALIS, RIMAE 325

Figure 8.42 (cont.)(b) Sirsalis and RimaeSirsalis, drawn by AndrewJohnson.

(b) LN.894


Figure 8.42 (cont.)(c) Sirsalis and RimaeSirsalis, another drawingby Andrew Johnson.

(c)

8.42 SIRSALIS, RIMAE 327

Figure 8.42 (cont.)(d) Rimae Sirsalis and DeVico A, drawn by RoyBridge.

(d)


Figure 8.42 (cont.)(e) De Vico A and thenorthern section of theRimae Sirsalis, drawn byRoy Bridge.

(e)

8.43 “STRAIGHT WALL” {RUPES RECTA} [22°S, 352°E] (WITH BIRT,BIRT A)

Properly known as Rupes Recta, this formation is so widely and popularly

known by its old name of the “Straight Wall” that I have entered it here

under that name.

One of Tony Pacey’s excellent photographs shows it well (Figure 8.43(a)).

Tony used his 10-inch (254 mm) Newtonian reflector and a 4 mm

Orthoscopic eyepiece to project the image onto FP4 film. The 1⁄2 second

8.43 “STRAIGHT WALL” (RUPES RECTA) 329

Figure 8.43 (a) The“Straight Wall” formation,more properly calledRupes Recta, pho-tographed by Tony Pacey.Appearing here as a thinblack line, the overlappingcraters Thebit, Thebit Aand Thebit L are just to itsleft and the small but dis-tinctive Birt, with Birt Aon its rim, is just to itsright. Other details givenin the main text.

(a)

330

Figure 8.43 (cont.)(b) Rupes Recta, photo-graphed using the 1.5 mreflector of the CatalinaObservatory in Arizona.Details in text. (CourtesyLunar and PlanetaryLaboratory.)

(b)

exposure was given at 1988 April 24d 22h 00m UT. At the time the Sun’s

selenographic colongitude was 356°.8.

Rupes Recta is situated near the eastern border of the Mare Nubium, just

west of the distinctive overlapping craters Thebit, Thebit A and Thebit L (see

Section 8.38). Tony Pacey’s photograph shows the general environs, includ-

ing the Thebit trio and Regiomontanus (upper-left corner) and Arzachel,

Alphonsus and part of Ptolemaeus (in the lower left). These areas are

detailed in Sections 8.38 and 8.4, respectively. The crater Pitatus is shown in

the upper-right corner of Figure 8.43(a) and this feature is described in

Section 8.32. Just west (right in Figure 8.43(a)) of Rupes Recta is a small but

distinctive crater, Birt, with a small crater on its rim, Birt A. Birt is a bowl-

shaped formation 17 km across and 3.5 km deep. Birt A has a diameter of

6.8 km and a depth of 1 km.

The “Straight Wall” is not particularly straight and it most certainly is

not a wall. It comes into daylight just after first quarter Moon and appears

as a thin black line when illuminated from the east (local morning). As

with most lunar relief features, it washes out near full Moon but then

appears as a thin light line towards the late afternoon, then being illumi-

nated from the west. This shows that there is a difference in height of the

ground to either side of it.

Despite appearances, the feature is not a shear cliff-face of extraordi-

nary height. Rather it is a fairly gentle slope linking the higher ground to

the east with the lower plain to the west. The average slope is of the order

of 7° and its height is not much more than 240 m. However the formation

is remarkable in view of its length, which is about 110 km.

What caused it? Is it a case of the ground to the east being uplifted, or

the ground to the west slumping downwards? Opinions are still divided

but the most popular view is that the ground to the east was buckled

upwards under compressional forces across this part of the Mare Nubium.

Take a careful look at Figure 8.43(a) and you should be able to discern

the outline of an almost entirely obliterated crater. Look at the border of

the terrae to the east of the Rupes Recta. Thebit actually lies across the old

rim. The lavas of the Mare Nubium have melted away most of its western

rim but traces of it can still be made out on the mare. You will see that

Rupes Recta spans much of the diameter of this old ‘ghost’ crater. Could

that be significant?

I will leave you to ponder on this intriguing formation but, to get you

started, you might like to consider the other buried ring at the southern

end of it and the rille that runs approximately parallel to it, a little to the

west and passing just beyond Birt. A close-up view is provided in Figure

8.43(b), which is a Catalina Observatory photograph, taken using the 1.5 m

reflector on 1966 May 29d 04h 41m UT, when the Sun’s selenographic colon-

gitude was 22°.6.

8.43 “STRAIGHT WALL” (RUPES RECTA) 331

8.44 THEOPHILUS [11°S, 26°E] (WITH CATHARINA, CYRILLUS, MÄDLER,MONS PENCK).

One of the most striking arrangements of craters on the Moon must be that

of Catharina, Cyrillus and Theophilus. They first come into sunlight about

5–6 days after new Moon and then present the spectacle shown in Figure

8.44(a). Figure 8.44(b) shows the area under a higher Sun. Even then the

grouping still looks impressive. The craters are shown lit from the opposite

direction in Figure 8.44(c), which is a view you will see about 19–20 days

after new Moon. The craters fill with shadow and are finally extinguished

at a lunar age of about 191⁄2 days (see Figure 8.44(d)).

In part, the dramatic appearance of the craters is heightened by the

scarp Rupes Altai framing the group to the west. The scarp is a raised ring

of mountains uplifted at the time of the impact that created the nearby,

and now lava-flooded Nectaris Basin. Cyrillus, Catharina and Theophilus

are thus sandwiched between the Mare Nectaris, to their east, and the

Rupes Altai, to their west. The rest of the Mare Nectaris region is discussed

in Section 8.30.


Figure 8.44 (a) Theophilus(bottom large crater),Cyrillus (above and adjoin-ing Theophilus) andCatharina (above Cyrillus),photographed by TonyPacey using his 10-inch(254 mm) Newtonianreflector on 1991 March21d. The approximate timeof the exposure was 20h UTand the approximate valueof the Sun’s selenographiccolongitude was 330°. The1⁄2 second exposure wasmade on T-Max 100 film,processed in HC110 devel-oper. The small crater onthe left of Theophilus isMädler, which is actuallysited on the mare Nectaris.

(a)

The southernmost of the trio of craters is Catharina. It is 97 km in diam-

eter. Its rough walls are very irregular in outline and heavily crater-spat-

tered. They reach up to 3.1 km above the crater. Notice the interior details.

There is a story here, but I will leave its investigation to you.

Catharina is clearly the most eroded, and thus the oldest, of the trio but

the middle crater, Cyrillus, is not much younger as far as lunar chronology

goes. Notice the apparent channel connecting Cyrillus to Catharina. In

reality the connection is the result of further impacts, though a degree of

ground-slumping is also evident.

Cyrillus is 93 km in diameter and is of similar depth to Catharina,

though its gentler interior slopes do give the impression of it being deeper

than it really is. Notice the prominent double-peaked mountain near the

centre of Cyrillus. It is instructive to compare the floors of the craters

8.44 THEOPHILUS 333

Figure 8.44 (cont.)(b) Theophilus and environs photographedusing the 1.5 m reflectorof the CatalinaObservatory on 1966September 3d 09h 19m UT,when the Sun’s seleno-graphic colongitude was130°.0. (Courtesy Lunarand Planetary Laboratory.)

(b)

(c)


Cyrillus and Catharina. What are their similarities and what are their dif-

ferences – and how do you explain them?

Obviously the youngest of the three craters is the 100 km diameter

Theophilus. It is a spectacular object in its own right, even divorced from

the presence of Catharina and Cyrillus (which it invades). The outer

flanks of this crater are very complex and the crater rim rises up to about

1.2 km above the level of its outer surrounds. The interior is rather deep,

extending to 3.2 km below the level of the outer surrounds. As the accom-

panying illustrations show, the interior slopes of Theophilus are very

complex. Clearly the initial terracing has been much degraded by local-

ised landslips. Notice the smooth central arena that surrounds the mag-

nificent central mountain cluster. The highest peaks of this complex soar

up to about 2 km above the level of the crater floor. I wonder when it will

be that a lunar mountaineer will climb the main mountain and from the

summit view the incredible spectacle of the surrounding unearthly land-

scape?

Various observers have noted odd appearances in Theophilus and many

consider it to be a ‘TLP hot spot’. I have never seen anything untoward in

it, myself.

At the position where the Rupes Altai passes closest to Theophilus is a

prominent mountain peak reaching further eastwards than the rest of the

range at this point. This feature is named Mons Penck and it is the subject

of the drawing by Andrew Johnson shown in Figure 8.44(d). Figure 8.44(e)

presents one of Terry Platt’s stunning CCD images of Theophilus.

The Mare Nectaris lavas encroach right up to the eastern flanks of

Theophilus and the significant crater to the east of Theophilus, called

Mädler, actually sits in the junction of the Mare Nectaris with the Mare

Tranquillitatis. It has a somewhat distorted outline, its diameter averaging

about 28 km. It is very deep for its size, measuring about 2.7 km vertically

from floor to rim.

Just a little north of this area of grand craters and spectacular moun-

tains is a little grouping of very small and apparently insignificant craters

that are, nonetheless, fascinating in their own right and may even hold a

secret or two. These are the subject of the next section.

8.44 THEOPHILUS 335

Figure 8.44 (cont.)(c) Evening approaches forCatherina, Cyrillus andTheophilus in this photo-graph taken by Dr T. W.Rackham with the 1.07 mreflector of the Pic du MidiObservatory in France.Notice how the terminatorfollows the outline of themare Nectaris. The onlyother detail available isthat the photograph wastaken before the end ofJuly 1964.


Figure 8.44 (cont.)(d) Theophilus, Cyrillusand Mons Penck, drawn byAndrew Johnson.

(d)

8.45 TORRICELLI [5°S, 28°E] (WITH CENCORINUS, MOLTKE, RIMAE

HYPATIA, TORRICELLI A, B, C, F, H, J AND K)Less than two hundred kilometres north of Theophilus, on the Mare

Tranquillitatis, is an interesting little group of features. These are shown

in Figure 8.45. This figure and Figure 8.44(b) in the previous section are

reproductions of parts of the same Catalina Observatory photograph and

the details are given in the previous section. (See the accompanying

caption to Figure 8.45 for the identification of the features listed.)

Despite its small size (about 20 km diameter), Torricelli does tend to

catch the eye because of its ‘keyhole’ shape. In fact it seems to be the fusion

of two craters, one smaller than the other.

The crater Cencorinus is only 3.8 km wide and yet it is very attention-

grabbing when seen under a high Sun. Its interior is very highly reflective

and it is surrounded by a patch of bright ejecta. It is normally written that

Aristarchus is the brightest crater on the Moon. Undoubtedly that is the

case when one takes into account its much larger size. Area for area,

though, I think Cencorinus is brighter when it is seen under the highest

angles of illumination. Cencorinus is probably one of the freshest craters

on the Moon that is big enough to resolve with a backyard telescope.

Another prominent, though much less brilliant, little crater is Moltke.

It is a bowl-shaped edifice with a diameter of 6.5 km and a depth of about

1.3 km. Space-probe images show it to have a razor-sharp rim and a bright,

smooth, interior. It also possesses a fairly bright ejecta nimbus. The eastern

end of the Rimae Hypatia passes between Moltke and the hinterland just

8.45 TORRICELLI 337

Figure 8.44 (cont.)(e) Theophilus. CCD imageby Terry Platt, using his121⁄2-inch (318 mm) tri-schiefspiegler reflectorand Starlight Xpress CCDcamera. Other details notavailable. The author hasapplied slight image sharp-ening and brightness re-scaling.

(e)

to the south of it. You might be able to see faint indications of it on Figure

8.45, though the lighting is not suitable to show it at its best.

The identified craters Torricelli A, B, C, F, H, J, and K have diameters of

11, 7, 11, 7, 7, 5 and 6 km, respectively. Of these, Torricelli B is particularly

interesting. Space-probe images show it to be rather conical in profile and

the interior is rather asymmetrically surfaced with deposits of varying

composition. In particular the Clementine images show a brilliant streak of

material (which I think is rich in feldspar – not enough room here for me

to explain why – though I do not at the present time know if this is the

official view) ‘splashed’ up the north-east interior from the centre to the

rim. Much of the south-west of the interior flank seems to be also, though

less richly, covered in the same material. This explains the brilliant ‘blob’

in the corresponding position that I have observed in this crater on many

occasions through my own telescopes.

Torricelli B seems to be one of the more definite TLP ‘hot spots’. It, and

the other craters around it, show variations in brightness and prominence

during the progress of a lunation. All perfectly normal and understand-

able. The crateriform aspect of Torricelli B is most obvious when the Sun

shines at a low angle over it and much of its interior is filled with shadow.

Under a higher Sun it becomes a greyish disk, brightest close to the time of

full Moon. Every so often, though, Torricelli B looks either much brighter

or much duller than one expects that it should at the given point in the


Figure 8.45 The ‘keyhole’crater Torricelli (topcentre), Cencorinus (brightcrater near bottom-leftcorner), and Moltke (brightcrater, two-thirds of theway down close to theright-hand side), pho-tographed by the CatalinaObservatory 1.5 mreflector. Same details asfor Figure 8.44(b). Thecrater half-way along a linebetween Torricelli andMoltke is Torricelli C.Notice the little arc ofcraters just above TorricelliC. From top to bottom thethree main ones areTorricelli K, J, and H. Ofthe two craters just to theleft of Torricelli, the largerone is Torricelli A and thesmaller one Torricelli F.Below these craters is thecrater Torricelli B, notableas the origin of manyrecent reports of TransientLunar Phenomena.(Courtesy Lunar andPlanetary Laboratory.)

lunation. I also find that its colour occasionally changes from its normal

white and takes on a very strong blue caste. When the colour is strong the

crater can even take on a purplish halo! I have also watched the crater errat-

ically varying in brightness with the variations happening on time-scales

of the order of minutes. Meanwhile the surrounding features, such as

the craters Moltke and Cencorinus stay sensibly constant in appearance.

Naturally any variations of the order of a second or two, and less, could well

be caused by atmospheric turbulence – but variations of brightness on

time-scales of minutes?

The BAA Lunar Section members have kept an eye on this crater since

the first anomalies were noticed in January 1983. In particular one

member, Mrs Marie Cook, has diligently observed Torricelli B visually and

with the use of coloured filters from then right up to the time of writing.

She has made many hundreds of observations of Torricelli B, using Moltke

and Cencorinus as comparisons. Her results do seem to confirm my impres-

sion of occasional erratic changes of colour and brightness and it is a pleas-

ure to pay tribute to her work here.

Are these changes illusory, or is there a real physical process happening

on the Moon? Certainly spurious colour and bad seeing conditions can,

and do, effect the appearances of features. I am sure that this is the correct

explanation for the vast majority of reports of supposed TLP. For instance,

the brilliant Cencorinus is often bedevilled by spurious colour (prismati-

cally created by the Earth’s atmosphere).

Sometimes Cencorinus shows an anomalous brightness change, as

occasionally does Moltke, though neither show significant colourations

other than that caused by spurious colour. An intriguing area of the Moon,

ripe for observation and research.

8.46 TYCHO [43°S, 349°E]As Figure 8.46(a) shows, the crater Tycho is an impressive formation when

seen under a low angle of solar illumination. Figure 8.46(b) is a drawing of

this crater made by Andrew Johnson and Figure 8.46(c) is one of Terry

Platt’s astounding CCD images. The crater is 85 km across and is very deep,

as lunar craters go. The vertical height of the crater rim above its deepest

point is 4.8 km. The interior terraces leading down from the rim to the

central arena are spectacular by any standards, as Figure 8.46(c) probably

shows best even though it was made under the conditions of a higher Sun-

angle. As one might expect, space-probe images show the crater in greater

detail. Figure 8.46(d) is a stunning view obtained from Orbiter V. The central

mountain massif soars upwards to a point 1.6 km above the crater floor.

As I said, the crater is spectacular enough when seen under a low angle

of illumination. If anything, it becomes even more so under a high Sun.

8.46 TYCHO 339

True, the interior relief disappears but the crater then becomes a white

disk with a brilliantly white ring marking the crater rim and an equally

brilliant ‘blob’ marking the central mountain. The crater itself is then sur-

rounded by a darkish halo. Beyond this commences a magnificent ray

system, which radiates across much of the Moon’s visible face (see Figure

8.46(e)).

The ray systems associated with craters had long puzzled selenogra-

phers and a wide range of theories were ‘cooked up’ to explain them. We

now know that they were generated by the impact explosion that created

each parent crater. The rays are composed of a very fine sprinkling of pul-

verised ejecta (mainly glassy beads) spattered ballistically across the Moon.

In the space of a few hundred million years the rays fade away because of

the effect of solar-wind bombardment, micrometeorite impacts and, par-

ticularly, the ‘gardening’ (churning) of the topsoil that results from micro-

meteorites and the diurnal thermal stresses.

Figure 8.46(f) was, despite its appearance, taken from Earth. In fact, a

Catalina telescope photographic image was projected onto a white sphere

and this was photographed, to produce a ‘rectified’ view of Tycho and its

rays. Note the zone of avoidance in the ray system, indicating the direction

of the incoming projectile that created Tycho.

The obvious rarity of large craters with ray systems lends support to the

idea that no large meteorites have struck the Moon for a very long time. In

fact, with the possible exception of the crater Giordano Bruno, Tycho is


Figure 8.46 (a) Tycho pho-tographed on 1967 January20d 01h 52m UT, using the1.5 m reflector of theCatalina Observatory inArizona. At the time of thephotograph the Sun’sselenographic colongitudewas 18°.5. (Courtesy Lunarand Planetary Laboratory.)

(a)

reckoned to be the youngest large crater on the Moon. One of the rays from

Tycho passes across the Apollo 17 landing site. It was from the samples

brought back that the nature of the rays was finally settled. Also the impact

that created Tycho was determined as having happened about 100 million

years ago.

There have been a number of reports of Transient Lunar Phenomena

associated with this crater but I have never seen anything I cannot explain

as being due to the conditions and/or lighting effects. One relevant obser-

vation of mine might be that of 1995 March 10d 22h UT (mid-time – I

observed for several hours). Using my 181⁄4-inch (0.46 m) reflector, at �144, I

could see that parts of the shadow inside the crater were not quite as deep-

black as the rest, see Figure 8.46(g). The effect was delicate but, nonetheless,

8.46 TYCHO 341

Figure 8.46 (cont.)(b) Tycho, drawn byAndrew Johnson.

(b)

too strong to be anything but real. I telephoned other BAA members and got

them to examine the black shadow in Tycho (but without revealing the

details) and was not surprised to get back confirmation.

How black are the shadows in craters? They certainly look very black

most of the time. However, if you were sitting in one of these shadow

regions you would certainly have no trouble in seeing details around you.

For one thing, there would be a weak glow thrown down by the stars in

the black sky. Much more than that, there would be a very bright Earth

shining down on you (if we can see your locale from the Earth, it follows

that you can see the Earth from where you are on the Moon). Also, and

this is the factor of relevance to my Tycho observation, you will be able to

see beyond the shadow-covered ground to the moonscape which is bril-

liantly illuminated by sunlight. I think the pools of slightly less deep-

black shadow in my Tycho observation were mostly created from light

reflected off the central mountains which were sticking up into the sun-

light, this being enhanced by the light reflected from the encircling

crater walls. Of course, the central peak also interrupted some of the light

reflected back from the far walls, hence the darker divide between the

two ‘grey’ regions. In how many craters can you see details within the

‘black’ shadows?


Figure 8.46 (cont.)(c) Tycho. CCD image byTerry Platt, using his 121⁄2-inch (318 mm) tri-schief-spiegler reflector andStarlight Xpress CCDcamera. No other detailsavailable. The author hasapplied slight image sharp-ening and brightness re-scaling.

(c)

8.46 TYCHO 343

Figure 8.46 (cont.)(d) Orbiter V image ofTycho. (Courtesy NASA andProfessor E. A. Whitaker.)

(d)


Figure 8.46 (cont.)(e) Tycho and its raysystem dominate this pho-tograph of the Moon,taken by Tony Pacey. Heused his 12-inch (305 mm)reflector to image theMoon onto Pan F film atthe telescope’s f/5.4Newtonian focus (no addi-tional optics used). The1/500 second exposure wasmade on 1992 November11d 21h 45m UT, when theSun’s selenographic colon-gitude was 100°.9.

(e)

8.46 TYCHO 345

Figure 8.46 (cont.)(f) Rectified image of Tychoand its ray system.(Courtesy Lunar andPlanetary Laboratory.)

(f)

8.47 WARGENTIN [50°S, 300°E] (WITH NASMYTH, PHOCYLIDES)This is the largest (84 km diameter) of a very rare breed of lunar craters indeed

– ones filled to the brim with basaltic lava. A CCD image of it by Terry Platt is

shown in Figure 8.47(a) and Figure 8.47(b) shows a drawing made by Andrew

Johnson that highlights the tree-like pattern of wrinkle ridges on its surface.

Wargentin is joined along its lunar southern edge by the vast (114 km diame-

ter) flooded crater Phocylides, while adjoining both is the overlapped (by both)

remnants of the once 77 km diameter Nasmyth. The whole grouping is best

seen a little before full Moon. Figure 8.47(c) and (d) show Wargentin together

with Nasmyth and Phocylides under this sort of lighting (details given in the

accompanying captions). I commend you to seek out Wargentin and have a

look at it yourself. It is strange to see this lunar ‘cup that runneth over’.


Figure 8.46 (cont.)(g) Tycho. Sketch by theauthor (details in text)showing the areas of ‘lessdeep-black’ shadow. Theeffect is here grossly exag-gerated for the sake ofclarity. In reality thepatches were very ill-defined and hard to see,scarcely lighter than thedeep-black shadow. At thetime of the observationthe value of the Sun’sselenographic colongitudewas 7°.8.

(g)

Figure 8.47 (a) Wargentin,imaged by Terry Plattusing his 121⁄2-inch(318 mm) tri-schiefspieglerreflector and StarlightXpress CCD camera. Theauthor has applied slightimage sharpening andbrightness re-scaling. Noother details available.

(a)

8.47 WARGENTIN 347

Figure 8.47 (cont.)(b) Wargentin, drawn byAndrew Johnson.

(b)


Figure 8.47 (cont.)(c) Wargentin (lower right),Phocylides (largest crater –upper left), and Nasmyth(large crater attached to,and overlapped by, bothWargentin andPhocylides), photographedusing the 1.5 m reflectorof the CatalinaObservatory. The photo-graph was taken on 1966January 6d 05h 45m UT,when the Sun’s seleno-graphic colongitude was80°.9. (Courtesy Lunar andPlanetary Laboratory.)(d) Wargentin, Phocylidesand Nasmyth, photo-graphed using the 1.5 mreflector of the CatalinaObservatory on 1967February 22d 03h 43m UT,when the Sun’s seleno-graphic colongitude was61°.0. (Courtesy Lunar andPlanetary Laboratory.)

(c)

(d)

8.48 WICHMANN [8°S, 322°E]In the previous 47 sections we have explored many formations replete

with spectacle and grandeur. I have deliberately finished this chapter

with a region of the Moon that seems obscure and even uninteresting to

the casual glance. Situated on the south-eastern sector of the Oceanus

Procellarum, the little (10.6 km diameter) crater Wichmann certainly

does not grab your attention as you peer through the telescope eyepiece.

8.48 WICHMANN 349

Figure 8.48 (a) Wichmannregion, drawn by AndrewJohnson.

(a)

However, what do you see when you look – when you really look? You

see all sorts of interesting detail – wrinkle ridges, chains of mountains,

the raised plateau on which the crater stands. Andrew Johnson has

looked – really looked. Figure 8.48(a) and (b) show two of his drawings.

What are the origins of these features? How do they relate to the Moon

as a whole?


Figure 8.48 (cont.)(b) Another study of theWichmann region of theMoon, by Andrew Johnson.

(b)

The point I am driving at is that the ‘old favourite’ Moon features may

have a great attraction but there is a great deal to be learned from the more

obscure areas. The whole of the surface of the Moon tells a story – the story

of how it all came to be as it is. I hope that you will feel inclined to investi-

gate the lunar surface for yourself – if so, you will find much of value in

some of its less ‘well-trodden’ regions.

8.48 WICHMANN 351

TLP or not TLP?

One of the few areas of study for the amateur lunar specialist that remains

of genuine scientific use is the highly controversial one of Transient Lunar

Phenomena (TLP – Americans use the term ‘Lunar Transient Phenomena,

LTP). The reason for the controversy is that a number of people have made

quite ridiculous claims of frequent weird happenings on the Moon’s

surface. The credibility of the subject has suffered greatly from the fanati-

cism of these people and others of the ‘lunatic’ fringe. Now, many people

dismiss the whole subject out of hand. Some go as far as to deride all who

would study the phenomena.

Most of the serious, long-term, students of the Moon – both amateur

and professional – are wisely cautious about supposed transient lunar phe-

nomena but accept that there is some evidence to support the view that

there is, at the very least, something worthy of investigation. I count myself

amongst their number. In this chapter I present some of the evidence and

explain how you might take part in this study yourself.

9.1 THE MYSTERY UNFOLDS

Observers, most significantly regular watchers of the Moon, report occa-

sional odd appearances, including short-lived glows (sometimes coloured)

and mist-like obscurations, involving small areas of the Moon’s surface.

This is not a new phenomenon. Indeed, reports go back centuries but by

the twentieth century, when it was established that the Moon has essen-

tially no atmosphere, most astronomers were of the opinion that all the

observed oddities could be explained as mere tricks of the eye.

However, a professional astronomer – Dr Dinsmore Alter – obtained

some hard evidence of something more than a simple illusion happening

on the Moon in 1955. He used the 60-inch (1.52 m) reflector at Mount Wilson

to photograph areas of the Moon in near-infrared and near-ultraviolet–

353

CHAPTER 9

violet–blue light. He did this by using appropriate filter and photographic

emulsion combinations. While all remained clear in the infrared photo-

graphs, he found that several of the UV–blue images showed a loss of detail

on part of the floor of the lunar crater Alphonsus. Some researchers won-

dered if Dr Alter had recorded the presence of a temporary mist emanating

from that part of the crater. Infrared light would penetrate a tenuous mist,

while the ultraviolet would not do so easily. A few amateur and professional

astronomers became interested. One of them was Nikolai Kozyrev, in Russia.

Kozyrev used the 50-inch (1.27 m) Cassegrain reflector of the Crimean

Astrophysical Observatory to take regular spectrograms of the Moon’s

surface. He monitored the Moon through the guiding eyepiece of the

spectrograph while he did so. His efforts were rewarded on 3 November

1958 when he obtained spectrographic evidence of a real physical transient

event at the Moon’s surface.

On that night he was conducting his normal programme when, at just

after 01h UT, he noticed that the central peak of the crater Alphonsus was

enveloped in a reddish haze. (See Section 8.4 for more about this crater,

including photographs of it.) He set the entrance slit of the spectrograph

across the image of the central peak of the crater and began taking spectra

while he continued to monitor the view through the guiding eyepiece (the

slit jaws being reflective, allowed guiding and the precise selection of the

part of the image sampled by the spectrograph).

During the next couple of hours Kozyrev saw the peak of Alphonsus

become very bright and white. Between 03h 00m and 03h 40m UT the appear-

ance of the crater returned to normal and Kozyrev ceased taking spectra.

When the spectrographic plates were processed several of them showed an

anomaly that afflicted the part of the spectrum – the stripe running

through the centre of it – formed by the light from the central peak.

Meanwhile the parts of the spectrum formed from the other parts of the

crater sampled by the slit showed nothing but the normal features of sun-

light reflected from the Moon’s surface. The spectra taken when the central

peak appeared bright showed strong emission bands. Actually these were

identified as being the ‘Swan Bands’ produced when molecular carbon

vapour, C2, is excited into emission. Other spectral features were present

(indicating other chemical components in the gas), blending with the spec-

trum of carbon. The last spectra taken showed that all had returned to

normal, in accordance with the visual impression.

Kozyrev’s observation aroused world-wide interest. You will find an

account of it in the February 1959 issue of Sky & Telescope magazine. It is

titled ‘Observation of a volcanic process on the Moon’, reflecting his inter-

pretation of what he had observed. Few others accepted this explanation,

even at the time.

354 TLP OR NOT TLP?

Kozyrev gives a more detailed account of his procedures, reductions

and conclusions in a paper ‘Spectroscopic proofs for existence of volcanic

processes on the Moon’ in The Moon – Symposium No. 14 of the International

Astronomical Union, edited by Kopal and Mikhailov for the Academic Press,

1962. Not an easy reference to obtain; perhaps an academic library/inter-

library loan service can obtain a copy for you. It is worth reading, even

though Kozyrev still gives his interpretation of volcanism in it. Most scien-

tists thought at that time (and still do today) that what Kozyrev had

recorded was the relatively quiescent effusion of a gas from the lunar

surface.

In the same book, Kozyrev’s paper is followed by another:

‘Microphotometric analysis of the emission flare in the region of the

central peak of the crater Alphonsus on 3 November 1958’, by A. Kalinyak

and A. Kamionko of the Pulkovo Observatory in Russia. The authors

conduct a detailed analysis of Kozyrev’s spectrum and conclude that the

event was indeed a gas release and the gas was excited to fluoresce under

the action of solar radiation. They conclude that the temperature of the gas

was less than 480 °C (maybe much less) and was of rather similar composi-

tion to the gas found in the heads of comets. They confirm the presence of

the Swan bands of carbon and deduce that the pressure of the gas was cer-

tainly less than one-hundred-millionth of a millimetre of mercury (this is

about one-hundred-thousand-millionth of the sea-level pressure of the

Earth’s atmosphere), and perhaps rather smaller than that.

There is a fascinating exposé of the American efforts to verify and

understand Kozyrev’s spectrum given in the October 1996 issue of Sky &

Telescope. The article is entitled ‘The lunar volcanism controversy’. The once

sceptical American astronomers, particularly the famous Gerard P. Kuiper,

changed their views when they eventually had the chance to study the orig-

inal spectrographic plates for themselves.

Some amateur and professional astronomers kept a watch on

Alphonsus for any signs of after-effects subsequent to the 1958 episode.

There were a few reports of red patches seen on the floor of the crater,

though no photographic evidence was ever secured (as far as I know!) and

nothing remained of them after some months had passed.

Kozyrev continued his programme of lunar observations and he ‘turned

up’ a couple more spectrographic anomalies – one in Alphonsus on 23

October 1959 and one in the crater Aristarchus (see Section 8.7 for more

about this crater) on 1 April 1969 – though the results were not quite as

definite as for the 1958 event. In the first, all that was identifiable was a

brightening at the red end of the spectrum. The spectrum of the Aristarchus

event sported the same general reddening but with bands of molecular

nitrogen and of the molecular species CN just about identifiable.

9.1 THE MYSTERY UNFOLDS 355

Astronomers Greenacre and Barr at the Lowell Observatory, USA, using

the 24-inch (0.61 m) refractor reported seeing intensely red and pink

coloured patches in the vicinity of the crater Aristarchus on 30 October

1963. They first saw the coloured glows at about 1h 30m UT. The glows

changed in intensity while the astronomers watched, disappearing after

about 25 minutes.

Further sightings of red glows were reported by an astronomer using

the 69-inch (1.75 m) reflector at the Perkins Observatory in the USA.

Many amateur groups, particular the Lunar Sections of the British

Astronomical Association and the Association of Lunar and Planetary

Observers (ALPO), began looking for TLP. Observers soon began reporting

anomalies. Undoubtedly many of these are explainable as being due to

things other than real events at the surface of the Moon (actually I think

the vast majority are not genuine TLP – more about this in Section 9.5) but

there are a number of instances which are not so easy to dismiss.

Barbara Middlehurst and her colleagues in the USA and Patrick Moore

in the UK were independently compiling catalogues of the reported

instances of TLP but they eventually published a combined catalogue in

1967. Patrick Moore updated it in 1971, the number of entries then stand-

ing at 713.

A pattern emerged from the hundreds of TLP reports. TLP were not dis-

tributed randomly. There seemed to be a preference for ‘events’ to occur

around the borders of the lunar maria and within certain craters. The high-

land areas were avoided. The crater Aristarchus came out as the ‘hottest’

TLP spot on the Moon with about a third of all reported events involving

this crater.

Aristarchus has even been the subject of a space-borne observation of

an anomaly. The three astronauts aboard Apollo 11 reported a glow localised

in the wall of the crater on 19 July 1969. At 18h 45m UT the crew could first

see an illuminated area to the north of the spacecraft. As they drew nearer

they confirmed their first impression that it was inside Aristarchus. Part of

the transcription of their communication to Mission control (it is difficult

to make out, so the transcription is incomplete) is:

It’s getting to be about zero phase. One wall of the crater (Aristarchus) seemsto be more illuminated than the others. It is definitely brighter than anythingelse I can see. It’s an inner wall of the crater . . . there doesn’t appear to be anycolour involved in it . . . it (is) the inner part of the west-north-west, the partthat would appear more nearly normal . . . looking at it from the Earth. . . .

Earth-based astronomers also confirmed the presence of the brightening,

as well as reporting other anomalies in Aristarchus on other dates around

the same time. Actually it was because of the earlier ground-based obser-

356 TLP OR NOT TLP?

vations that the astronauts were asked to keep a look out for anything

unusual.

During the Apollo 16 mission Ken Mattingly, in the orbiting Command

Module, witnessed several flashes from the lunar surface (though I do not

have any further details about this) and Apollo 17 astronaut Harrison

Schmidt witnessed a flash emanating from the region of the lunar crater

Grimaldi. This is another TLP ‘hot spot’. See Section 8.20 in Chapter 8 for

more about this crater.

Another TLP hot spot (at least it was in the 1960s and 1970s, even if

rather less so since then) is the crater Gassendi. See Section 8.22 for photo-

graphs and details about it. Transient bright points of light were seen by

Walter Haas (10 July 1941) and H. P. Wilkins (17 May 1957) but the most sig-

nificant ‘event’ involving Gassendi occurred on 30 April 1966. First detected

by P. K. Sartory, for about four hours a reddish wedge-shaped streak was

seen to span the central peak to the south-west rim of the crater. Several

independent observers witnessed this phenomenon. One of these was

Patrick Moore and he describes it as “the most unmistakable red event I

have ever seen on the Moon”.

Back in those days there was an assumption that all TLP should appear

as red glows. One BAA Lunar Section member, Peter Sartory, designed a

device, called a ‘Moonblink’ which consisted of a unit containing red and

blue filters that was plugged into the telescope before the eyepiece. Turning

a knob brought either filter into the optical path. By manually alternating

between the red and blue filters while watching through the eyepiece, any

red patch on the Moon would appear light when seen through the red filter

but would show up as darker when seen through the blue filter. Many posi-

tive ‘blinks’ were obtained by observers using this arrangement.

Meanwhile, in the USA, a network of professional astronomers was set

up under the auspices of NASA using more sophisticated versions of this

device (utilising an electronic detector rather than a human eye – see the

July 1967 issue of Icarus for an account of this work).

One of the team, Winifred S. Cameron, has been involved in research

into TLP for decades (and she still is, though now retired) and is widely

regarded as the world’s foremost authority. She is a prolific author of

papers and articles on the subject. One reference you might especially like

to seek out is an article, entitled ‘Lunar Transient Phenomena’, in the

March 1991 issue of Sky & Telescope.

One of the cases she cites in the article involves the crater Pitatus (see

Section 8.32 for illustrations and for details about this crater) and she

shows two photographs taken by Gary Slayton of Fort Lauderdale, Florida,

of a bright ‘blob’ in the crater which moves between the time the two

photographs were taken (the times are not given, though the date was 5

9.1 THE MYSTERY UNFOLDS 357

September 1981). This is not the only instance of moving lights on the

Moon being reported by Earth-based observers.

Returning to the subject of the ‘blink’ devices, there are problems with

them. In particular, spurious colour, described later, is an effect which has

its cause in the Earth’s atmosphere and many ‘blinks’ were undoubtedly

due to this, rather than anything real on the Moon. Eventually observers

realised that the majority of TLP were actually not even red, only a minor-

ity of visual anomalies showing any significant colour at all. Blink devices

have now rather gone out of fashion.

Since I have only room enough to cite a few examples of TLP, I think this

would be a good point to interrupt this potted history to summarise the

main types of the visual anomalies observed.

9.2 CATEGORIES OF TLP

The following are the types of visual anomaly most often reported. In each

case the area of the Moon affected is usually only a few kilometres square.

Short-term albedo changesThese are unusual increases or decreases in the apparent brightness of the

Moon’s surface. The change might last for a few hours, though mostly for

rather less than a hour. Sometimes the change occurs and then is fairly

steady – say the brightness of a small patch of the Moon increases, then

remains at roughly the same elevated level for a while only then to stead-

ily decrease back to the normal value once more. At other times the bright-

ness pulsates. When this happens the brightness usually varies rather

erratically. These brightness fluctuations can happen on time-scales as

short as a second or two.

Obscurations of surface detailsA small patch of the Moon might appear blurred or indistinct while the sur-

rounds remain sharp and clear-cut. The effect often lasts for about an hour.

Significantly, the blurring sometimes is seen to start out very localised and

distinct but then spreads out, becoming less obvious as it does so – almost

like a cloud of vapour thinning out.

Coloured effectsSometimes coloured effects are seen as an accompaniment to brightness

changes, or to surface obscurations. Sometimes coloured effects are seen

on their own. Most observed anomalies do not show significant colours.

However, there have been rare instances when the colours have been very

vivid. In my own experience, regions showing short-term brightness

changes tend to show a bluish tint if any colour is visible at all.

358 TLP OR NOT TLP?

Flashes of lightThese are the rarest of all reported TLP. However, there are too many reli-

able reports to dismiss them. They appear as bright (sometimes very bright)

flashes of light or brief twinkles of light against the Moon’s surface. At least

two photographs show apparent flashes, though I must say that any one of

a host of photographic faults could well be the true explanation for them

– let alone other (less probable) explanations such as a glint of reflected

sunlight from a satellite that happened to pass through the field of view at

the time the photograph was taken! Occasionally flashes are seen along

with other types of TLP in progress.

9.3 THE MYSTERY CONTINUES

The growing interest of amateur and professional astronomers in

Transient Lunar Phenomena through the 1950s and 1960s continued into

the 1970s. Unfortunately, as I said in the introduction, the subject also

attracted more than its fair share of cranks. These people tended to go

to their telescopes and see all manner of coloured effects, plumes of

smoke erupting from craters, etc. Many rushed into print with half-baked,

and ill-informed, ideas about the mechanisms producing these physical

phenomena.

I only wish I could say that this sad state of affairs was entirely in the

past, but I cannot. There are still some today for whom the Moon is a fair-

ground of amazing phenomena. Not only do these people bring the deri-

sion of many astronomers on the whole subject, their ‘reports’ pollute the

data, making any serious study difficult. It is for that reason that I give low

weighting to the results of statistical studies based on the complete TLP

databases. Various links, such as with the solar activity cycle, with the posi-

tion of the Moon in its orbit (and so the passage of the Moon through the

Earth’s magnetotail), with moonquake activity, etc., all have been variously

‘proved’ and ‘disproved’ by researchers.

Fortunately we do have some good evidence and data. As you would

expect, it is the work of the professional astronomers which is taken

most seriously. For instance, astronomers of the Tokyo Astronomical

Observatory have conducted many long-term studies of the Moon’s surface

brightness and the way the Moon’s surface polarises the incident sunlight

it reflects (some vibration angles of the light-waves are reflected more than

others).

In 1970 they observed an event involving Aristarchus which they

described in The Moon – issue 2 (1971). Their paper is entitled ‘An anomalous

brightening of the lunar surface observed on March 26, 1970’, and is

authored by Naosuke Sekiguchi. While on their normal programme of

photometric (brightness) and polarimetric observations with a 36-inch

9.3 THE MYSTERY CONTINUES 359

(0.91 m) reflector, Sekiguchi and co-workers found, on that date, the region

around Aristarchus became 0.3 magnitude brighter than normal. At the

same time its colour index decreased by 0.1. In other words, as well as

becoming over 30 per cent brighter, the region became significantly

bluer. The change in optical polarisation that was recorded only in the

Aristarchus region also adds weight to the assertion that a genuine TLP was

recorded. In his paper, Sekiguchi refers to some of the many other papers

which detail other professional observations of this phenomenon. He also

suggests that the TLP he recorded may be related to a major solar flare that

occurred 29 hours before his observation.

I will finish this ‘potted history’, sketchy as it is, with the briefest pos-

sible account of my own involvement in TLP research and a summary of the

‘state of play’ at present.

In 1979, after returning to live in my parents’ home (in Seaford, East

Sussex, UK) at the end of my undergraduate years, I joined the Lunar Section

of the British Astronomical Association and straight away resumed making

lunar observations with my 61⁄4-inch and 181⁄4-inch reflecting telescopes.

There existed a ‘telephone alert network’ whereby an observer reported any

suspect appearances to a central co-ordinator. The co-ordinator then con-

tacted all the available active observers who had joined the network. In the

years that followed I observed the Moon whenever I could, through changes

of home and occupation. I arrived in Bexhill-on-sea, in East Sussex, in 1983.

My observational work continues to this day, though a long-term illness has

reduced the amount I can manage to do in recent years.

I responded to many ‘alerts’ in those years. In some cases I could not

confirm any visual anomaly. In some I could, though most often conclud-

ing that the effect was caused by a mechanism other than anything hap-

pening on the Moon (see Section 9.5 for more about this). In a few instances,

there seemed to be something genuinely anomalous at the surface of the

Moon. I instigated a few ‘alerts’ myself, though in some of these cases I sus-

pected (but could not be sure of) causes other than a genuine TLP. I should,

perhaps, make it clear that the person providing the alert would never give

more than the general location of the supposed ‘event’. Any corroboration,

or otherwise, was sought after the event by checking the written reports

and any accompanying sketches.

My eventual location in Bexhill proved expedient when the opportu-

nity arose to be a guest observer at the Royal Greenwich Observatory, just

a twenty-minute drive away. Thanks to introductions by Patrick Moore, and

because I am qualified as an astronomer, I was afforded the very great priv-

ilege of using the RGO’s equipment. From January 1985 to March 1990 I had

the run of the ‘Equatorial Group’ of telescopes and additional facilities in

the main buildings. My main purpose there was to repeat Kozyrev’s efforts

in the hope of obtaining a good-quality spectrum of a TLP in action.

360 TLP OR NOT TLP?

The main instrument I used was the 30-inch (0.76 m) coudé reflector with

its elaborate high-dispersion spectrograph (Figure 9.1). Another useful instru-

ment there was the 36-inch (0.91) Cassegrain reflector in the adjacent dome.

I used to set up both telescopes for lunar observing sessions. The Cassegrain

reflector was better for monitoring purposes (Figure 9.2) and it took but

moments to move through the adjoining corridors from one to the other.


Figure 9.1 The 30-inch(0.76 m) coudé reflector atthe Herstmonceux site ofthe former RoyalGreenwich Observatory.The light from the tele-scope emerges from thedoor in the back of thetelescope tube to be inter-cepted by the mirror at thetop of the tall tripodalgantry. The light is thenpassed down into the headof the spectrograph. Thevarious parts of the spec-trograph are arranged onthree floors of the build-ing!

Of course, I took many standard spectra for comparison purposes with

the hope of recording the spectrum of a TLP in action. The equipment

would now be considered old-fashioned, in that the spectra were recorded

on 7-inch�1-inch(178 mm�25 mm) photographic plates – which I had

to cut from standard 10-inch�2-inch stock of Kodak IIaO plates, subse-

quently processing them after the exposures were made in the telescope’s

362 TLP OR NOT TLP?

Figure 9.2 The author canbe seen below the 36-inch(0.91 m) Cassegrainreflector at theHerstmonceux site of theformer Royal GreenwichObservatory.

spectrograph. Today’s newly graduated astronomers would consider this

a quaint art practised in a bygone age!

Figure 9.3(a) shows a print I made from one of the plates. Some details

are given in the accompanying caption but suffice it to say here that you

can see it is of very high spectral resolution. I scanned the plates using the

RGO’s temperamental plate density scanning instrument (PDS) which pro-

duced 3 metre long tracings (plots of intensity versus wavelength) from

each plate. A very small part of one of these is shown in Figure 9.3(b). The

tracings allowed for detailed measurements of any spectrum I suspected of

showing an anomaly. For a fuller description of the equipment and proce-

dures see the July–September 1987 issue of Astronomy Now magazine.

Now the big question – did I spectrographically record a TLP? I am afraid

I did not.

On 27 September 1985 I was busy in the dome of the 30-inch (0.76 m)

telescope when a ‘TLP alert’ came through by telephone. The seeing was

extremely bad and I had already taken a standard spectrum of Aristarchus.

In response to the alert I set the telescope so that Torricelli B, the subject

of the alert – suspected variations of brightness – was on the slit. Actually

this was difficult to do since it was nearly invisible in the violently

unsteady seeing. I made the required exposure (9 minutes in that case).

When I processed the plate, and subsequently scanned it, I found that it

contained nothing but the usual spectrum. I must say that there was little

hope of success on that night, even if Torricelli B was undergoing a genuine

TLP, as only for a very small amount of the exposure was the light from this

small crater actually dropping through the entrance slit of the spectro-

graph. Most of the time the turbulent distortions made Torricelli B miss

the slit and so the spectrum was mainly built up from the light of the sur-

rounding moonscape.

The next night a thick fog hung over Bexhill and I decided to stay at

home. However, the telephone rang – there was another ‘TLP alert’, again

concerning Torricelli B. After a hazardous drive to the observatory I set up

the equipment and gave the plate a much longer exposure than normal (to

try and offset the effects of the fog). Even so, the processed and scanned

plate proved useless; no anomalies were detectable, save the ‘noise’ gener-

ated by the thinness of the image.

Frustratingly, one of the few periods the RGO telescopes were not avail-

able to me because of other usage coincided with some significant TLP activ-

ity. All I could do was to use my own telescopes. One of these instances

concerned Torricelli B. On 31 May 1985 I was using my 0.46 m reflector

when, at 20h 23m UT, I noticed that Torricelli B was bright and mauve

coloured and sported a mauve ‘halo’. I ran inside and telephoned the co-

ordinator. At 20h 29m UT I was back at the eyepiece but the colour had gone!


364 TLP OR NOT TLP?

(a)

The crater seemed to be pure white in hue and varying erratically in bright-

ness, with a mean period judged to be about 2 seconds. The ambient seeing

conditions caused a general lapsing of focus with a mean period estimated

at about 5 to 10 seconds, while the turbulent rippling of the image had a

period of about half a second. At 20h 34m UT I noted that the crater had taken

on an intermittent pinkish tinge. From then until close of observations at

22h 18m UT I noticed definite variations in the apparent brightness of the

crater that seemed not to be the result of the atmospheric conditions. The

two other observers in the BAA Lunar Section available under clear skies

that night independently recorded similar brightness and colour varia-

tions, along with ‘star-like flashes’ occurring inside the crater. They agree to

the nearest minute about the times of the flashes. I saw no flashes.

The most significant TLP I have ever witnessed occurred the day before

this one. Patrick Moore, in company with Paul Doherty, noticed an anom-

alous brightening of the west wall of Aristarchus, plus some blurring on

the north-west wall. Myself and another five members of the BAA Lunar

Section were alerted and observed this crater (remember – no details of the

anomaly were ever passed on during an alert; merely the general location

of the suspected anomaly).

I had bad seeing conditions but by 20h 53m UT I noticed that in brief

flashes of good imaging a pink tinge was present along the northern sector

of the crater interior. At 22h 08m UT I noticed that there was an odd appear-

ance to the shadow on the north-west wall (see Figure 9.4) – a notch formed

in it! By 22h 54m UT an intense ruby-red colouration developed on the inside

of this ‘notch’. The seeing deteriorated to the point that I had to pack up

by 23h 08m UT. All who took part agreed on most of the points about the

anomaly, and the timings – and two others agreed with me about the

‘notch’ in the interior shadow – and all the reports were entirely indepen-

dently made!

My anguish about not having the use of the RGO telescopes on those

two nights was intense. There were other frustrating occasions when


Figure 9.3 (a) High-resolu-tion spectrum of sunlightreflected from the surfaceof the Moon, taken by theauthor, using the 30-inch(0.76 m) coudé reflectorand high-dispersion spec-trograph of the RoyalGreenwich Observatory.The wavelength rangecovered is approximately355 nm (left-hand side ofthe bottom strip) to504 nm (right-hand side ofthe top strip), the wave-length increasing from leftto right along each strip.There is a small amount ofoverlap between each strip.Above and below the mainspectrum is a copper–argon emission spectrumexposed on the plate at thesame time as the Moonspectrum for calibrationpurposes.(b) A small part of a tracingfrom the spectrum. Thetwo broad dips in the spec-trum of moonlight (uppertrace) correspond with thebroad calcium (Ca) absorp-tion features indicated atthe right-hand end of thesecond strip from thebottom in (a).

(b)

‘TLP alerts’ were telephoned to me but the skies were not clear over

Herstmonceux. So, I had failed to secure a spectrum of a TLP in action.

Nonetheless, I enjoyed myself immensely using the professional telescopes

for those five years and I did conduct other successful observational pro-

jects with them. It was a great experience and it only came to an end when

the RGO moved to Cambridge. More recently, the RGO has closed down alto-

gether – a piece of Britain’s scientific heritage cast into the garbage can by

our politicians.

For me, it was back to the backyard telescopes. I did build a spectro-

graph onto my largest telescope (Figure 9.5 – and see my book Advanced

Amateur Astronomy for a fuller description) but the illness I have already

mentioned was beginning to tighten its grip and I found myself able to do

less and less observing. Nonetheless, amid changes to the BAA Lunar

Section I even took over as co-ordinator of the TLP observing group, which

by then was flagging for various reasons. I managed to re-activate the group

but, after a few years, had to give up this work also.

The present situation is that there are a few scattered groups active

around the world in the field of TLP observation and study, though I cannot

say that there is as much enthusiasm as there once was. There are excep-

tions. ALPO, for instance, conduct energetic observing programmes. The

BAA Lunar Section continues with the TLP work, though with fewer active

members than it had in its heyday.

I wish there was space to give more examples of TLP observations, par-

ticularly those recorded by professional astronomers. However, I hope I

have said enough to whet your appetite. Of course, the burning question

arising from all this is – what causes Transient Lunar Phenomena?

366 TLP OR NOT TLP?

Figure 9.4 A visualanomaly recorded by theauthor in Aristarchus (seetext for details).


Figure 9.5 (a) The spectro-graph the author builtonto his 181⁄4-inch (0.46 m)reflector can be seenarranged along the back ofthe 8-feet long tube of thetelescope.(b) Spectrum of sunlightreflected from the Moon,obtained by the author,using his spectrograph.

(a)

(b)

H� H� Calcium H� H�

9.4 WHAT MIGHT BE THE CAUSE(S) OF TLP?If we only ever had one genuine TLP, the example which Kozyrev observed

and recorded the spectrum of in 1958, I would have concluded that Kozyrev

had witnessed the after-effects of a small piece of cometary material strik-

ing the Moon at, or very close to, the central peak of Alphonsus. I would

have reckoned that the explosively uplifted surface materials produced the

initial reddish cloud. When this cleared it might have left the gases from

the vaporised impactor to fluoresce under the solar radiation (the sunlight

plus the solar wind bombardment).

However, we do not just have the one TLP. Hundreds have been recorded.

The greatest difficulty with the comet impact theory is explaining why it

is that certain locations on the Moon’s surface seem especially prone to

TLP. Surely cometary impacts, if they were the correct explanation, should

produce a random distribution of TLP-type events?

Could it be that the Moon has, at least in certain locations, large quan-

tities of sub-surface comet-type ices and these are released through

fissures? This seems wildly improbable. True, there has been some surface

ice apparently detected by the Lunar Prospector probe near the polar regions

(the jury is still out on this interpretation of the received reflectance data)

but comet-type ices below the surface over much of the globe is quite

another thing. Most planetary scientists/geologists would react to such a

notion with great hilarity.

Much more reasonable is the case for radioactive gases and the rem-

nants of gases left over from the Moon’s more volcanically active ancient

past emanating through fissures from deep below the surface. Interest-

ingly, the seismometers left on the Moon have provided data which indi-

cates that TLP sites tend to lie above moonquake epicentres (though see my

earlier note of caution about supposed statistical correlations).

I also think that the solar wind and radiation from the Sun might play

a part in producing TLP. Simple calculations show that the average solar-

wind flux conveys insufficient energy to produce any visible manifesta-

tions at the surface of the Moon. However, the solar wind is very gusty and

the most intense blasts do convey sufficient energy. I have already referred

to Sekiguchi’s observation of 26 March 1970, and the fact that he draws

attention to a major solar flare that occurred 29 hours earlier as the pos-

sible source of the fluorescence he recorded.

Certainly this fluorescence might just be in the surface rocks. In fact,

we have long known that there is more to moonlight than simply

reflected sunlight. A really significant study of this was undertaken by the

‘Manchester Group’ in the 1960s. Z. Kopal’s article in the May 1965 issue

of Scientific American is well worth the trouble of obtaining. He, along with

T. W. Rackham, photographically recorded a number of luminous events

368 TLP OR NOT TLP?

at Pic du Midi. Some of the photographs are presented in the article. The

lunar craters Copernicus, Kepler, Plato, and Aristarchus were particularly

affected. At times, temporary enhancements in brilliance up to about 80

per cent of that due to the incident sunlight were detected. Later work

suggests that the Moon normally shines about 10 per cent brighter than

is due to reflected sunlight alone. Kopal presents a detailed analysis in his

article and concludes that corpuscular radiation from the Sun is respon-

sible.

It is worth noting that not everybody accepts that the Kozyrev 1958

spectrum is the result of a gas release. For instance E. J. Öpik, in Advances in

Astronomy and Astrophysics, Volume 8 (1971) (edited by Z. Kopal), points out that

the region of bright emission did not encroach into the part of the central

peak of Alphonsus in shadow. The demarcation visible on the spectrum is

sharp, which is not what one would expect from a cloud of gas. Öpik con-

cludes that fluorescence from the solid lunar surface occurred, rather than

any gas emission.

I have great faith in the lunar-rock fluorescence theory as the explana-

tion for many TLP. However, I still wonder if gas effusion from the lunar

surface also forms part of the story. For instance, we know for sure (as a

result of the Apollo missions) that radon gas escapes from below the lunar

surface. The Apollo Alpha Particle Spectrometers (AAPS) aboard the Apollo

15 and Apollo 16 Command Modules – which orbited the Moon while two of

the crew worked on the lunar surface – detected alpha particles with the

particular energy spectrum which links them to the radioactive decay of

radon gas.

Even better, three American scientists, Paul Gorenstein, Leon Golub and

Paul Bjorkholm, have conducted a detailed analysis of the AAPS results and

found that the sites of maximum emission coincided with the established

‘hot spots’ of TLP (this correlation, at least, seems strong enough to be

definite!). Their paper ‘Radon emanation from the Moon, spatial and tem-

poral variability’ is presented in The Moon, 9 (1974). Grimaldi, Alphonsus and

the edges of the lunar maria figure particularly highly. They found that the

largest recorded radon emissions occurred from the area of Aristarchus –

the ‘hottest’ spot of the lot!

It strikes me as plausible that any effusing radon gas might be excited

into fluorescence in the same way as for the surface rocks. Perhaps other

gaseous species are brought up along with the radon gas.

The solar-wind particles would cause the gas to fluoresce by colliding

with the gas atoms/molecules and causing electrons in the atoms to be tem-

porarily excited to higher energy levels. When they de-excite, the electrons

hop down the energy level rungs in the atoms, so producing a characteris-

tic spectrum. This is the way a conventional fluorescent lamp works (such

9.4 WHAT MIGHT BE THE CAUSE(S) OF TLP? 369

as a sodium street-light). Interestingly, like sodium vapour, radon gas pro-

duces a nearly monochromatic spectrum. The main emission in the visible

spectrum occurs at a wavelength of 434.96 nm (multiply this figure by 10

if you prefer wavelengths expressed in ångstrom units). This is in the

blue–violet part of the spectrum.

Expressing my thoughts rather crudely, if the Sun ‘sneezed’ an extra

strong gust of solar-wind particles and the ‘spray’ arrived at the Moon just

as a particular location ‘burped’ radon gas, then the interaction between

them could easily lead to the sort of blue fluorescent effect that has been

observed in features such as Torricelli B.

I also conjecture that if the gas release was particularly ‘violent’

(though still very feeble by terrestrial standards) then maybe some of the

finest (perhaps colloidal-sized) particles could be swept up from the lunar

surface to produce a temporary obscuration over a small area of the Moon.

Of course, the local topography would determine whether or not a cloud

of dust could be raised by a gas escape. One might expect this gas cloud to

be either white or to appear reddish in hue, depending on the sizes of the

levitated particles. The light scattered by the cloud would also be partially

polarised, the extent of the polarisation depending on the particle sizes.

Finally, ionised gas atoms/molecules in motion (and particularly those

interacting with fine solid particles in suspension or motion) could lead to

charge separation and a resultant build-up of electrical potential differ-

ence. The eventual discharge through the gas (a form of sheet lightning)

might well account for the rarely observed bright flashes and sparkles.

So much for my theories as to the causes of genuine TLP. I may well be

completely wrong. We still need much more data.

Other people have differing ideas, such as piezoelectric discharges from

the Moon’s surface due to stresses and strains in the surface rocks caused

by the diurnal temperature changes, and triboelectric discharges, again

caused by the piezoelectric effect but with moonquakes providing the

stresses and strains. Winifred Cameron provides an extensive review of TLP

in her paper ‘Lunar Transient Phenomena (LTP): manifestations, site distri-

bution, correlations and possible causes’ in Physics of the Earth and Planetary

Interiors, Volume 14 (1977).

One thing I am sure of is that genuine TLP are rare. From my experience

I would say that the vast majority of the observed anomalies are nothing

to do with any real physical process at or near to the surface of the Moon.

For explanations of these we need to look much nearer home.

9.5 POSSIBLE CAUSES OF BOGUS TLP

There are three sources of the spurious reports of TLP. These are: the Earth’s

atmosphere; the telescope; the observer. There are a number of different

370 TLP OR NOT TLP?

mechanisms operating in each of these sources. Any one, or a combination,

of these can result in what I call ‘bogus TLP’.

The atmosphereOne of the major pitfalls for the observer is the presence of spurious colour.

The Moon’s image is composed of light–dark boundaries. You will often

see these fringed with colour. We are all familiar with the effect a trian-

gular glass prism has on a thin beam of white light passing through it. The

light is deviated by the prism in a direction towards its base. The light is

also sorted into its component wavelengths (colours), the amount of devi-

ation being slightly different for each of the component colours. We call

this effect dispersion. The violet rays are bent slightly more than the red

ones.

The Earth’s atmosphere acts rather like a prism orientated with its

base uppermost. As well as astronomical objects being slightly elevated –

making sunrise happen slightly early and sunset happen slightly late –

their light-rays are slightly dispersed as a result. Obviously, for each

light–dark boundary in the image a full ‘rainbow’ is produced. However,

the orientation of the boundary and the image structure of its immediate

surrounds play a part and usually only a section of the full ‘rainbow’ is

visible. For instance, most lunar craters appear with a bluish fringe along

their southern rims, the opposite rim being fringed with red. Plato often

shows this effect, though many craters do not show both the half-rainbows

with equal prominence. In the case of Plato the red colouration along the

northern rim is usually more obvious than the blue colour fringing the

southern rim. Some craters, for example Aristarchus, normally display

spurious colour of the opposite orientation; blue to the north and red to

the south.

This spurious colour effect is usually greatest when viewing the Moon

(or other celestial body) when it is low over the horizon. However, it also

varies with the ambient atmospheric conditions: temperature, humidity,

air pressure and the presence of aerosols and particulates.

The implications for TLP hunting are obvious. Time and time again that

‘red glow’ enveloping a lunar feature (crater wall, central peak, etc.) will

turn out to have been generated by our atmosphere. I would urge you to get

to know what coloured effects are usual for a given feature. I have already

mentioned Plato and Aristarchus. Another interesting example is the

crater Lassell. On many nights, especially near full Moon, Lassell seems

enveloped by a bluish haze, while the mountain mass just a short distance

to the north-west seems to be covered by an orange glow.

Image turbulence, or more properly scintillation, is also a real nuisance.

Sometimes the image is soft but fairly steady. At other times it is undulating

9.5 POSSIBLE CAUSES OF BOGUS TLP 371

violently. Most often the two effects occur together. Again, the result is dif-

ferent for different lunar features. Has part of the crater wall really ‘gone

soft’ or is it just that the fine terracing present at that location has run

together to give a blurred or ‘foggy’ appearance? There is no substitute for

experience when it comes to deciding whether a real anomaly might be

present.

The telescopeNo telescope is perfect. Even putting aside any mechanical faults, the

optical system will have its limitations, both in design and in manufactur-

ing tolerances. I cover some points in Chapter 3 but lack of space here

causes me to refer you to my book Advanced Amateur Astronomy for a much

fuller and more detailed discussion of telescope optics, their faults and

some ways of evaluating and correcting them.

Suffice it to say here that lateral chromatic aberration (colour-fringing)

is usually the most misleading error experienced by the TLP observer.

Longitudinal chromatic aberration manifests as a general softening of the

image when seen near the centre of the field of view. Away from the centre

it becomes the lateral form. Observations made with refractors could be

suspect because of this but, in the main, it is the telescope’s eyepiece which

usually produces the worst effect. In that sense, you might experience the

greatest trouble if using a reflector of low focal ratio!

Critically examine your eyepieces in use. Do you find that the

light–dark boundaries in the image, for instance along the edge of a

shadow-filled crater, become fringed with colour as you move the telescope

to place the crater near the edge of the field of view? This is classic lateral

chromatic aberration. Near the centre of the field of view the image will

probably appear colour-fringe free. If you have some high-quality coloured

filters try the effect of using them. Does the image seem to sharpen when

using the filter? If so, you can be fairly sure that the image is being

degraded by the presence of longitudinal chromatic aberration.

The remedy is either to stick to making monochrome observations

using coloured filters, or to invest in eyepieces with better correction.

The observerWe all make mistakes. Our eyes are imperfect and the brains behind them

are even more so. When you consider how the complex lunar vista changes

with lighting it is not hard to understand how the observer can be caught

unawares by apparently strange appearances. Most times those ‘strange

appearances’ turn out to be quite normal for particular lighting angles and

seeing conditions. Yet again, experience is the key to deciding whether the

way a feature appears to you is truly anomalous or not.

372 TLP OR NOT TLP?

9.6 TLP OBSERVING PROGRAMME

As far as telescope requirements go, use what you have got. Once in a while

an apparent anomaly will appear which is prominent enough to be seen

through a small telescope, so it is difficult to put a definite lower limit to

the size of telescope required. Obviously, though, anything larger than 6-

inch (152 mm) aperture is desirable, provided it is of good quality. Reflectors

are normally to be preferred over refractors, provided they have eyepieces

that are well corrected for chromatic errors (see the foregoing notes).

If you are a novice observer, it is essential that you first observe through

a few lunations to gain some knowledge of what the Moon really looks like

under various lighting angles. Even then, I would recommend concentrat-

ing on just one or two specific features and only expand your repertoire

when you have gained enough experience to be sure what you are looking

at really is normal or not. Perhaps the notes in Chapter 8 of this book may

help you get started.

When I go to the telescope to carry out TLP hunting, I adopt a definite

strategy. Though this might vary depending on the conditions, I normally

split observing sessions into two main activities. First I use a low power

(�144 on my 0.46 m telescope) and I ‘raster-scan’ the whole of the lunar

surface, both the sunlit and the darkened hemispheres. This might take

about 15 minutes. By ‘raster-scanning’ I mean east–west sweeps across the

lunar surface, for each sweep setting the telescope a little higher in decli-

nation. The bands swept out then overlap a little, ensuring full coverage. I

carefully scrutinise all the lunar features as they pass through the field of

view, looking for any abnormalities.

I then carefully scrutinise any features which I think look suspicious.

Perhaps I might momentarily leave the telescope to check charts or photo-

graphs of the area in question (under as similar lighting as possible).

Obviously, I might keep the area under scrutiny for a while – one can still

be flexible within one’s ‘plan of action’.

Assuming all is normal, as it is the vast majority of times, I then spend

some time examining other specific features. My list includes: Aristarchus,

Torricelli B, Plato, Proclus, Alphonsus, Messier and Messier A, Tycho. All

these are TLP ‘hot spots’. Not all will be in sunlight at any one time (except

near full Moon) but some features, especially Aristarchus, can often be

located in Earthshine.

I then proceed to re-scan the Moon with higher magnifications, spend-

ing some time to re-scrutinise my selected features, and so on as the session

continues. Most nights I do not increase the magnification beyond �207,

anyway, because of the turbulent seeing conditions. If the image you are

looking at is at all ‘soft’, then there is certainly no point in going to greater

powers.

9.6 TLP OBSERVING PROGRAMME 373

Obviously there is a real danger of observational selection by concen-

trating on specific features. At least making scans of the rest of the lunar

surface will tend to dilute this effect.

Keeping a watch for TLP during lunar eclipses is especially useful. Some

people speculate that the rapid changes in surface temperature may

trigger TLP.

I recommend joining a society with a TLP observing group. Then if sus-

picions are aroused you can telephone a central co-ordinator with your

suspicion – but only give the general location, otherwise you might prej-

udice the subsequent analysis. The co-ordinator can then raise an ‘alert’

among the other participating members.

You can do valuable work just by visually scanning for TLP. If you can

also use other techniques you may be able to make an outstanding contri-

bution. Photography (see Chapter 4), video techniques and CCD imaging

(see Chapter 5) are obvious extensions of purely visual work. You could

include the use of coloured filters with all the imaging methods.

Photometry is possible (especially with video/CCD images saved on a com-

puter). With colour filters in use this becomes colorimetry – the relative

brightness in specific wavebands. Use a polarising filter and you can do

polarimetry. If you can build or obtain a spectrograph you could follow in

the steps of Kozyrev. For details of these more advanced techniques could I

refer you to my book Advanced Amateur Astronomy, as I have already exceeded

the page allocation set by the publisher for this one!

I have enjoyed observing the Moon for three decades. Despite my current

incapacity, I can still do some telescopic observation and I am hoping to do

much more again as my fitness improves in the future. Maybe I can go

another three decades at the telescope eyepiece? At any rate, I feel sure that

I will live long enough to see humans walking on the lunar soil once more.

In this book I have tried to ‘shoehorn’ as much useful information into

the available space as possible. Nonetheless, the treatment is far from com-

plete. This book could be twice as long and still not cover everything. We

already know so much about our Moon. Yet there is still much more to

learn. I hope, though, I have said enough to persuade you to obtain what-

ever telescope you can and turn it to the Moon. You will find a world of fas-

cination and mystery among the dramatic mountain ranges and the eerie

plains and craters. I hope you will experience for yourself the Moon’s “mag-

nificent desolation”.

374 TLP OR NOT TLP?

aberrations (optical) 51, 52, 58, 372Abineri, Keith 146, 317achromatic object glass 51Achromatic Ramsden eyepiece see

eyepieces (telescope)Aestuum, Sinus see Sinus AestuumAgarum, Promontorium see

Promontorium AgarumAgrippa (lunar crater) 168–71Albategnius (lunar crater) 152, 158–9albedo 34Aldrin, Edwin 1, 125, 128–9Alpes, Montes seeMontes AlpesAlpes, Vallis see Vallis AlpesAlpetragius (lunar crater) 161–4Alphonsus (lunar crater) 152, 153,

161–4, 331, 354, 368, 369, 373Altai, Rupes see Rupes AltaiAlter, Dr Dinsmore 353Anders, William 128anorthosite 134anorthositic gabbro 136annular eclipse 13Ansgarius (lunar crater) 260–5Apenninus, Montes seeMontes

Apenninusapochromatic object glass 52, 54, 56Apollomissions 1–2, 128–32, 133, 135,

136, 161, 166, 176, 195, 208, 235, 246,247, 273, 341, 356–7, 369

apparent magnitude (limitingtelescopic) 23–4

Archerusia, Promontorium seePromontorium Archerusia

Archimedes (lunar crater) 246–56Ariadaeus (lunar crater) 168–71Ariadaeus, Rima see Rima AriadaeusAristarchus (lunar crater) 40, 152, 171–7,

355, 356, 360, 365, 366, 369, 373Aristarchus plateau 40, 171, 175, 222Aristillus (lunar crater) 246–56Aristoteles (lunar crater) 152, 177–8Armstrong, Neil 1, 125–9Arzachel (lunar crater) 161–4, 311, 331Arzachel, Rimae see Rimae ArzachelASA number see ISO numberascending node see nodes (orbital)Association of Lunar and Planetary Observers

(ALPO) 366astigmatism see aberrations (optical)

Atlas (lunar crater) 204–8Atlas A (lunar crater) 204–8atlases (lunar) see alsomaps of Moon 69,

70, 71Autolycus (lunar crater) 246–56

Babbage (lunar crater) 299–302Bailly (lunar crater) 152, 179–81, 187Bailly A, B (lunar craters) 181Barlow lens 57–8, 84, 85–6barycentre 3basalts seemare basaltsbasins (lunar) see also under specific names

138, 140, 179, 187, 237, 239, 246, 249,255, 271, 299

bays, lunar see SinusBean, Alan 130Beaumont (lunar crater) 271–6Beer, W. (and Mädler, J. H.) 43, 44, 175Belkovitch (lunar crater) 204–8Bianchini (lunar crater) 246–56Birt (lunar crater) 331Birt A (lunar crater) 331Birt, W. R. 45Bjorkholm, Paul 369blooming of lenses 57Bonpland (lunar crater) 208–13Borman, Frank 128Bouvard, Vallis see Vallis Bouvardbreccias 136Brewer, David 117Bridge, Roy 65, 201, 206, 208, 229, 253,

264, 265, 266–7, 278, 279, 285, 287,290, 303, 305, 311–12, 314, 327, 328

Briggs (lunar crater) 311–16Briggs A, B (lunar craters) 311–16British Astronomical Association (BAA) 44,

45, 146, 191, 317, 339, 342, 357, 365,366

breccia 136Bullialdus (lunar crater) 152, 181–4Bullialdus A, B (lunar craters) 182, 183

Cadogan, Peter 142, 238Cameron, Winifred S. 357, 370Carpatus, Montes seeMontes CarpatusCassegrain telescope 42, 54, 55, 81, 361,

362Cassegrain–Newtonian telescope 64Cassini, J. D. 180, 184, 194

375

INDEX

Cassini (lunar crater) 152, 184–7, 251Cassini A, B (lunar craters) 184catadioptric telescopes 52, 53, 54, 55,

81, 148catena 37Catharina (lunar crater) 332–7Cattermole, Peter 138Caucasus, Montes seeMontes CaucasusCavalerius (lunar crater) 37, 225–32celestial sphere 7Cencorinus (lunar crater) 337–9Cernan, Eugene 132Chacornac (lunar crater) 296–9charge-coupled devices (CCDs) 26,

99–106, 109, 111, 118, 161, 184, 186,202, 204, 206, 218, 219, 285, 335,337, 342, 346, 374

Chevallier (lunar crater) 204–8chronology, lunar see lunar chronologyClarke, Ivor 146Clavius (lunar crater) 37, 152, 187–90,

270Clavius C, D, J, K, L, N (lunar craters)

187–90Clementinemission 47, 132, 133, 143, 146,

159, 175, 317, 320, 323, 338Cleomedes (lunar crater) 198–204, 213Cobra’s Head, The 176Cognitum, Mare seeMare Cognitum Collins, Michael 128–9colour-difference photography 40–1,

290–1coloured filters 95–7, 353, 357–8, 372,

374colour index 360colour, spurious see spurious colourcolour vision 40, 175, 203, 263–4, 290coma see aberrations (optical)computer-controlled telescopes 27, 52computer processing of images 104, 106,

115, 116, 117–18, 119–20, 121–3,161–2

Conon (lunar crater) 164–8Conrad, Charles 130Cook, Jeremy 71Cook, Marie 339colorimetry (lunar surface) 374Copernicus, N. 4, 190Copernicus (lunar crater) 37, 140, 152,

190–7, 232, 233, 369craters (general) see also under specific

crater names 35–7, 38–9, 137–8, 140,164, 178, 235–6, 309

Crisium, Mare seeMare CrisiumCyrillus (lunar crater) 332–7Cysatus (lunar crater) 269–70

Daguerreotype 69da Vinci, Leonardo see Leonardo da VinciDaniell (lunar crater) 296–9

Danjon scale 10Dantowitz, R. 116, 117dark current 102dark frame 105dark halo craters 161Dawes (lunar crater) 290–6Dawes Limit 50detector quantum efficiency (DQE) 101 de la Rue, Warren 69descending node see nodes (orbital)depth measurements of lunar craters

see lunar crater shadowmeasurements

diffraction limit 48–50, 60Digges, Thomas 29distortion see optical aberrationsdiurnal libration 17, 18Dobbins, Thomas 117, 123dodging (photographic technique) 95,

96domes (lunar) 37–8, 154, 222, 232–5Dopplemayer (lunar crater) 235–43dorsa 34, 36–7Draper, J. W. 69drawing the Moon 47–8, 61–7drives (telescope) 25, 53Duke, Charles 132

Earthshine 4, 6, 7, 25, 80, 83, 84, 373eclipses 4, 5, 8, 9, 10, 11, 12, 13, 80, 83,

374ecliptic 8, 10Eddington (lunar crater) 311–16ejecta see rays (lunar surface) also

secondary craterseffective focal length 74, 77, 79, 81,

84–93, 106, 114effective focal ratio 58, 59, 77, 78, 84–93,

106, 114, 246Egede (lunar crater) 177–8electronic imaging see CCDsElger, T. G. 45, 191Endymion (lunar crater) 152, 204–8,

213, 260ephemerides 147Epidemiarum, Palus see Palus

Epidemiarumequation (personal) see personal

equationEratosthenes (lunar crater)140, 164–8,

249, 253Eudoxus (lunar crater) 177–8Euxinus, Pontus see Pontus EuxinusEvans, Ronald 132eyepieces (telescope) 51, 57–8, 59, 84,

86–7, 89–92, 105, 372

Fabricius (lunar crater) 256–60feldspar 134, 338films (photographic) see photographic

376 INDEX

filters see coloured filtersflat field 105fluorescence 2, 368–70 Foecunditatis, Mare seeMare

FoecunditatisFra Mauro (lunar crater) 152, 208–13Fracastorius (lunar crater) 271–6frame-grabber 115–16Fraunhofer (lunar crater) 213–19Furnerius (lunar crater) 152, 213–19, 260Furnerius B, J (lunar craters) 213–19

Gagarin, Yuri 128Galileo 4, 29gardening 136, 340Gargantuan Basin 238Gassendi (lunar crater) 37, 235–43, 298,

357Gassendi A (lunar crater) 235–43, 298Gilbert, William 29Giordano Bruno (lunar crater) 340Golden Handle 248, 255Golub, Leon 369Goodacre, Walter 44Gordon, Richard 130graben 160, 171, 244–5grain (photographic) see photographicGreenacre and Barr (Lowell Observatory)

356grid system see lunar grid systemGrimaldi (lunar crater) 126, 127, 225–32,

357, 369Grimaldi, Francesco 30Gruemberger (lunar crater) 269–70 Gruithuisen, P. (and ‘lunar city’) 152,

219–22Guericke (lunar crater) 208–13

Hadley Rille, see Rima HadleyHaise, Fred 130Harbinger, Montes seeMontes HarbingerHarriott, Thomas 29Haas, Walter 357Hatfield, Commander H. R. (and lunar

atlas) 19, 71, 151Helicon (lunar crater) 246–56Heraclides, Promontorium see

Promontorium HeraclidesHercules (lunar crater) 204–8Herodotus (lunar crater) 171–7Herschel (lunar crater) 161–4Herschel, William 42, 171Hesiodus (lunar crater) 279–82Hevelius, J. (Hewelcke, J.) 30, 226, 283Hevelius (lunar crater) 152, 225–32Hill, Harold 66Hipparchus (lunar crater) 158–9Holden (lunar crater) 260–5Hortensius (lunar crater and associated

domes) 38, 152, 232–5

Humboldtianum, Mare seeMareHumboldtianum

Humorum Basin 253, 236, 238, 299Humorum, Mare seeMare HumorumHuygens, C. 40Huygenian eyepiece see eyepieces

(telescope)Hyginus (lunar crater) 243–5Hyginus, Rima see Rima HyginusHypatia, Rimae see Rimae Hypatia

International Astronomical Union (IAU) 20,35, 140, 213

International Lunar Occultation Centre (ILOC)22, 27

International Occultation Timing Association(IOTA) 22, 27

image resolution see resolutionimage-scales 74–5, 81, 84, 92, 105–6, 114Imbrium Basin 140, 168, 184, 246, 250,

252–5, 273, 283Imbrium, Mare seeMare ImbriumInternet 146–7Iridum, Sinus see Sinus IridumIrwin, James 131

Jansky (lunar crater) 276–9Janssen (lunar crater) 152, 256–60Johnson, Andrew 62–3, 64–5, 66–7, 170,

187, 188, 193, 194, 220–1, 224, 226,227, 228, 230, 239, 242, 254, 255,279, 280, 281, 290, 293, 295, 300,304, 305, 315, 318, 319, 325, 326,335, 336, 339, 341, 346, 347, 349–50

Julius Caesar (lunar crater) 168–71Jura, Montes seeMontes Jura

Kapteyn (lunar crater) 260–5Kästner (lunar crater) 260–5Kellner eyepiece see telescope eyepiecesKepler (lunar crater) 196, 197, 265, 369key map of Moon 152Klein (lunar crater) 158–9König (lunar crater) 181–4Kopal, Z. 70, 368–9Kozyrev, N. 354–5, 360, 368Krafft (lunar crater) 311–16KREEP 134, 211Kuiper, G. P. 70

La Pérouse (lunar crater) 260–5LacusMortis 31–2Somniorum 296–9

Lamé (lunar crater) 260–5Langrenus 30Langrenus (lunar crater) 40, 152, 213,

260–5, 267Langrenus A (lunar crater) 260–5Leonardo da Vinci 4

INDEX 377

Laplace, Promontorium seePromontorium Laplace

Lehmann (lunar crater) 316–20librations (general) 15–19, 20, 62, 204libration in latitude 17, 18, 19libration in longitude 17Lick (lunar crater) 198–204Linné (lunar crater) 44Liverpool Astronomical Society 45Loewy, M. 69, 70Lohrmann (lunar crater) 225–32Lohrmann, Wilhelm 43, 44Lohse (lunar crater) 260–5Longshaw, Nigel 65, 210, 211, 212, 213,

215, 216, 217, 240, 297, 299, 309, 310,311

Lovell, James 128, 130Lubiniezky (lunar crater) 181–4luminescence see fluorescenceLunamissions 126, 128, 133, 137lunar city see Gruithuisen, P. (and ‘lunar

city’)lunar craters see craters see also under

specific crater nameslunar crater shadow measurements

140–50lunar eclipses see eclipsesLunar Excursion Module (LEM) 128–9,

130, 131, 132, 273lunar grid system 178lunar mare seemarelunar occultations see occultationsLunar Prospectormission 47, 133, 136,

142, 143, 368Lunar Orbitermissions see OrbitermissionsLunikmissions see LunamissionsLunokhod 126, 128

Maestlin (lunar crater) 265–7Maestlin R (lunar crater) 152, 265–7Mädler, J. see Beer, W. (and Mädler, J. H.)Mädler (lunar crater) 332–7magnification (telescopic) 33, 40, 57,

58–9, 164, 373Mairan (lunar crater) 62, 64–5Manchester Group 70maps of the Moon see also atlases (lunar)

29–30, 40–5, 150–1, 152–3, 156mare (general) see also under specific names

30, 138, 140, 142, 154, 369MareCognitum 126, 208Crisium 32, 152, 198–204, 213, 260Foecunditatis 267Frigoris 159, 177, 283Humboldtianum 204–8Humorum 152, 235–43, 244, 302Imbrium 30, 37, 128, 140, 152, 159,160, 168, 187, 238, 246–56, 283, 289

Nectaris 152, 260, 271–6, 332, 335

Nubium 181, 241, 279, 302, 331Orientalis 126, 140–1, 273Serenitatis 30, 44, 128, 161, 249,290–6

Tranquillitatis 30, 40, 129, 168, 256,271, 290–6, 337

Vaporum 168, 245mare basalts 134, 136, 140, 234, 235–8,

240, 242, 246–8, 251, 252, 265, 275,276, 283, 293–5, 331

mascons 142Mattingly, Thomas 132, 357Mayer, Tobias 42Menelaus (lunar crater) 290–6Messier and Messier A (lunar craters)

152, 267–9, 373Metius (lunar crater) 256–60Middlehurst, B. 356Mitchell, Edgar 131, 208Miyamori Valley 229Miyamoto, Professor S. 70Mobberley, Martin 11, 13, 84, 89, 117Moltke (lunar crater) 337–9monocentric eyepiece see eyepieces

(telescope)MonsPenck 332–7Pico 37, 256, 283–90Piton 37, 66, 256, 283–90

MontesAlpes 66, 159, 160, 177, 184, 249, 250,251, 283

Apenninus 37, 131, 152, 164–8, 248,249, 250, 251

Carpatus 37, 249, 250Caucasus 177, 186, 249, 250, 251Harbinger 152, 222–5Jura 246–56Teneriffe 284, 289

moonblink device 357–8moonquakes 135–6Moore, Patrick 45, 138, 140, 356, 360, 365Moretus (lunar crater) 152, 269–70Mortis, Lacus see Lacus Mortismotor drives see drives (telescope)mountains, lunar seeMontes andMons

NASA 1 (facing page), 70, 127, 130, 131,132, 133, 139, 140, 146, 147, 174, 197,242, 268, 288, 306, 323, 343, 357

Nasmyth, James (and Carpenter, James)44, 190–1

Nasmyth (lunar crater) 346–8Nebularum, Palus see Palus NebularumNectaris Basin 260, 271, 273Nectaris, Mare seeMare NectarisNeison, Edmund 44Neper (lunar crater) 152, 175, 276–9Newtonian reflecting telescope 2, 42,

53, 54, 56, 59, 81, 84, 87

378 INDEX

nodes (orbital) 8, 10Nubium, Mare seeMare NubiumNyquist theorem 105–6

object glasses (telescope) see telescopesalso refracting telescopes

Oceanus Procellarum 31, 126, 127, 130,171, 175, 190, 222, 232, 238, 246,251, 255, 265, 311

oculars see eyepieces (telescope)occultations 22–7Öpik, E. J. 369optical accuracy see aberrationsorbit (of Moon) 2–19Orbitermissions 127, 146, 159, 176, 197,

216, 242, 243, 269, 305, 317Orientalis Basin 140, 246, 324, 339, 343Orientalis, Mare seeMare OrientalisOrthoscopic eyepiece see eyepieces

(telescope)

Pacey, Tony 7, 31, 32, 33, 34, 35, 167, 168,191, 193, 196, 197, 198, 214, 215, 246,247, 261, 271, 291, 296, 298, 329,332, 334

PalusEpidemiarum 241, 244, 302Nebularum 184Putredinis 164–8Somnii 31

Parry (lunar crater) 208–13Peirce (lunar crater) 198–204Peirce B (lunar crater) 198–204Penck, Mons seeMons Penckpenumbra 8, 9personal equation 27Petavius (lunar crater) 213–19, 260phases of Moon 4–5, 30, 31, 32, 33, 34,

35, 79, 82Phocylides (lunar crater) 346–8photographiccamera focusing 81, 84, 90developing 93–5enlargement 74, 84–93exposure lengths 76, 77, 78, 80, 82,83, 91–2, 93

field of good definition 86–7, 88, 90–1films 71–4, 75, 78, 79, 80, 83, 84, 92,120, 246, 298, 329, 354, 362

grain 72–3, 91, 94guiding 92–3resolution 72–4, 84, 86, 91, 92tolerance to undriven exposures 75–6,82

dodging 95, 96photometry 359–60, 374Picard (lunar crater) 198–204Piccolomini (lunar crater) 271–6Pickering, W. H. 69, 186Pico, Mons seeMons Pico

Pitatus (lunar crater) 152, 279–82, 357Piton, Mons seeMons PitonPlato (lunar crater) 37, 152, 256, 283–90,

369, 373Plato A (lunar crater) 283–90Plato Zeta (slump feature) 283, 285Platt, Terry 118, 119, 120, 121–3, 161,

163, 194, 218, 219, 285, 335, 337,339, 342, 346

Plinius (lunar crater) 152, 290–6polarimetry (lunar surface) 359–60, 374Porter (lunar crater) 187–90Posidonius (lunar crater) 37, 152, 296–9Posidonius A (lunar crater) 296–9Plössyl eyepiece see eyepieces (telescope)position angles 22–3Prinz (lunar crater) 222–5Proclus (lunar crater) 198–204PromontoriumAgarum 32, 152, 156–7, 202, 203Archerusia 290–6Heraclides 246–56Laplace 246–56

Ptolemaeus (lunar crater) 161–4, 331Puiseux, P. 69, 70Purbach (lunar crater) 306–11Putredinis, Palus see Palus PutredinisPythagoras (lunar crater) 152, 299–302

Rackham, Dr T. W. 39, 70, 201, 335radon emissions from Moon 243,

369–70Ramsden (lunar crater) 152, 302–6Ramsden, Rimae see Rimae RamsdenRamsden eyepiece see eyepieces

(telescope)Rangermissions 126, 138, 139, 208Rayleigh’s resolution limit 50, 105rays (lunar surface) 37, 175, 196, 197,

203, 255, 265, 269, 295, 340–1refracting telescopes 23, 41, 51, 52, 54,

55, 81, 219Regiomontanus (lunar crater) 152,

306–11, 331Regiomontanus A (lunar crater) 306regolith 136resolving powerof CCDs 105, 106–7, 109of photographic films seephotographic

of telescopes 48, 49, 50, 105, 106 seealso photographic

of video 106, 109, 111, 114, 115Rheita (lunar crater) 256–60Rheita, Vallis see Vallis RheitaRiccioli, Giovanni 30, 35, 190rilles (general) 39, 40, 42, 160, 161, 170,

171, 176, 222, 243–5, 288, 295, 298,302–6, 324–8

rilles (specific) see Rima and Rimae

INDEX 379

RimaAriadaeus 152, 168–71Hadley 39, 131, 166Hyginus 152, 170, 243–5Hypatia 337–9Sirsalis (also Rimae Sirsalis) 152,324–8

Triesnecker 243–5RimaeArzachel 39Ramsden 302–6Sirsalis (also Rima Sirsalis) 152, 324–8

Rogers, Gordon 118, 184, 186, 202, 204,206

Roosa, Stuart 131Ross (lunar crater) 290–6Rosse (lunar crater) 271–6Rosse, Lord 175Royal Greenwich Observatory (RGO) 2, 360–6RupesAltai 39, 271–6, 332, 335Recta 39, 152, 311, 329

Russell (lunar crater) 152, 311–16Rutherfurd (lunar crater) 187–90

Saros 13–14Sartory, Peter 357Saturn 5 rocket 128, 129Schickard (lunar crater) 152, 316–20Schiller (lunar crater) 89, 152, 320–3Schmidt, Harrison 132Schmidt, Julius 43, 44, 175Schmidt-Cassegrain telescopes see

catadioptric telescopesSchröter, J. H. 42–3Schröter’s Valley see Vallis SchröteriSchröteri, Vallis see Vallis SchröteriScott, David 131secondary craters 42, 194–5secondary spectrum 51seidal errors see aberrations (optical)Sekiguchi, Naosuke 359–60Selenographical Society 45selenographic co-ordinates (definition)

20, 21Selenotopographische Fragmente 42Seleucus (lunar crater) 311–16Serenitatis Basin 299Serenitatis, Mare seeMare SerenitatisShepard, Alan 131, 208Short (lunar crater) 269–70sidereal period 4Silberschlag (lunar crater) 168–71SinusAestuum 164–8Iridum 31, 246–56, 299Medii 168

Sirsalis (lunar crater) 324–8Sirsalis A (lunar crater) 324–8

Sirsalis, Rima see Rima SirsalisSirsalis, Rimae see Rimae SirsalisSlayton, Gary 357solar eclipses see eclipsessolar wind 2, 171, 340, 368, 369–70Somniorum, Lacus see Lacus SomniorumSouth Pole–Aitken Basin 132–3spectrography (of Moon) 354, 360–7spurious colour 40, 176, 204, 286, 358,

371“Straight Wall” see Rupes Rectastructure of Moon 135–7Struve (lunar crater) 311–16Sudbury, Patrick 70Surveyormissions 126, 130Swigert, John 130synodic period 4

teleconverters 77, 89telescopes see also Cassegrain telescope

and Cassegrain-Newtonian telescopeand catadioptric telescope andNewtonian telescope and refractingtelescope 2, 23, 24, 33, 37, 40, 41,42, 43, 47, 48–56, 148, 286, 354, 356,359–60, 361–3, 366–7, 372, 373

telescope eyepieces see eyepieces(telescope)

telescope mirrors 52, 54, 59Teneriffe, Montes seeMontes TeneriffeTheaetetus (lunar crater) 184–7Thebit (lunar crater) 306–11, 331Thebit A,L (lunar craters) 306–11, 331Theophilus (lunar crater) 152, 332–7tides 14–15, 16TLP see Transient Lunar PhenomenaTimocharis (lunar crater) 246–56tri-schiefspiegler telescope see telescopesTolles eyepiece see eyepieces (telescope)Torricelli (lunar crater) 152, 337–9Torricelli A, C, F, H, J, K (lunar craters)

337–9Torricelli B (lunar crater) 337–9, 363–5,

370, 373Transient Lunar Phenomena (TLP) 11,

154, 163, 168, 176–7, 186–7, 203, 243,285–8, 289, 290, 335, 338–9, 341–2,353–74

Tranquillitatis Basin 292Tranquillitatis, Mare seeMare

TranquillitatisTriesnecker (lunar crater) 243–5Triesnecker, Rima see Rima Triesneckertube-currents (telescope) 53–4Tycho (lunar crater) 37, 152, 339–46,

373

umbra 8, 9unsharp masking see photographic

380 INDEX

valleys see VallisVallisAlpes 152, 159–60, 249Bouvard 39Rheita 39, 256–60Schröteri 39, 171–7, 244

Vendelinus (lunar crater) 213, 260–5video imaging 26–7, 99–100, 106–17vignetting 59–60, 81–2, 86, 89Viscardy, Georges 71visual response of eye 51, 101Vitello (lunar crater) 235–43

Wallace (lunar crater) 164–8Walter (lunar crater) 306–11Wargentin (lunar crater) 152, 346–8

water on Moon 133Whitaker, Professor E. A. 37, 39, 70, 127,

139, 140, 174, 197, 218, 242, 268, 277,288, 306, 343

Whipple, J. A. 69Wichmann (lunar crater) 152, 346–51Wilkins, H. P. 45, 140, 357Wolf (lunar crater) 181–4Worden, Alfred 131wrinkle ridges 34, 36–7, 237, 241, 255,

295, 346

Yerkes (lunar crater) 198–204Young, John 132

Zondmissions 126

INDEX 381

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